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Nagano · Komoro

Komoro Castle

小諸城

Komoro, Nagano

CastleHilltop castle (hirayamajiro)Japan's 100 Fine Castles No. 26

What makes this castle distinctive

To reach this castle you walk down from the town, not up: Komoro is a "hole castle."

Why?

Castles usually stand above their towns, but Komoro Castle sits lower than its castle town. It uses deep ravines at the foot of Mount Asama as dry moats, and a cliff above the Chikuma River guards its west side. Komoro is said to be the only castle of this "hole castle" (anajiro) type in Japan.^[5][11]

Three things not to miss

San-no-mon, the gate at the park entrance

Where: The entrance to Kaikoen Park, a short walk from Komoro Station.
What to look at: How the two-story gate spans the stone walls on either side, the small openings in the flanking walls for arrows and guns (sama), and the "Kaikoen" plaque on the front.
Why it's interesting: Washed away in the great flood of 1742, the gate was rebuilt around 1765–66 and is an Important Cultural Property. Unlike the rough natural stones of the main enclosure, the walls beside it are made of cut stones fitted tightly together (kirikomi-hagi). The plaque was written by Tokugawa Iesato, head of the Tokugawa family after the shogunate.^[3][7]
Can you see it?: Visible from outsideVisible freely from outside; the paid area of the park begins once you pass through.

The rough-stone base of the lost keep

Where: The northwest corner of the main enclosure (honmaru).
What to look at: A stone base one level higher than the rest of the main enclosure's walls, built of larger natural stones stacked as they are.
Why it's interesting: In Sengoku Hidehisa's time a three-tiered keep (tenshu) roofed with gold-leaf tiles is said to have stood here. It burned after a lightning strike early in the Kan'ei era (1626), and without permission from the shogunate it was never rebuilt. Only the stone base remains.^[6][11][15]
Can you see it?: Visible from outsideInside the paid area of Kaikoen Park.

The Otemon, across the railway tracks

Where: Otemon Park on the east side of Komoro Station, across the station and tracks from Kaikoen Park.
What to look at: A plain, sturdy two-story gate with thick pillars and a large hip-and-gable roof.
Why it's interesting: Built by Sengoku Hidehisa in 1612 as the castle's main gate, it is said to have been called the "tile gate" because tiled roofs were rare then. After the Meiji era it served as a restaurant and as a temporary schoolhouse for the Komoro Gijuku academy, and was later donated to the city and restored to its Edo-period look. It is an Important Cultural Property.^{[4][8][9][14]}
Can you see it?: Partly visibleThe gate is open all day and free to see. The upper floor opens only on set days (10:00–15:00, free).

At a glance for visitors

Nearest station: 3 min walk from Komoro Station
Climb: Not confirmed
Time neededEditors' estimate: About an hour to walk around the park; about two hours if you also visit the museums. The Otemon is a few minutes' walk away on the other side of the station.
Admission: Walking ticket: 300 yen (high school and up), 100 yen (elementary/junior high). Combined ticket (grounds, zoo, Chokokan, Toson Memorial Museum, Koyama Keizo Art Museum, Komoro Gijuku Memorial Hall): 500 yen / 200 yen (groups of 20+: 400 / 150 yen). Free for preschoolers with a guardian.
Hours: Park 9:00–17:00. Chokokan, the Toson Memorial Museum and the Koyama Keizo Art Museum: April–November 9:00–17:00, December–March 9:00–16:30 (last entry 16:00)
Access: Open to visitors
Kaikoen Park, inside San-no-mon, needs a ticket (walking ticket or combined ticket). The Otemon is outside the park and open all day. Wheelchairs cannot enter through the Suigetsu ticket gate because of steps at Suigetsu Bridge.

Checked: 2026-10-03

View on map Open in Google Maps Kaikoen Park website (Komoro City)Komoro Castle Ruins - Kaikoen Park (Komoro Tourism Bureau)

The story of this castle

Historical record

A castle below its town

Komoro Castle makes full use of the land as it slopes from Mount Asama down to the Chikuma River. Deep ravines, cut by water into the volcanic deposits of Asama (a landform called tagiri), serve as dry moats, and the cliff above the Chikuma River guards the west. As a result the castle sits lower than its town, which is why it is called a "hole castle."^[5][11][15]

Tradition

Takeda Shingen laid out its shape

Before the castle, the Oi clan had strongholds here in the Muromachi and Sengoku periods. In 1554 Takeda Shingen of Kai Province took Komoro, and according to Komoro City he saw how important the area was and had his retainers Yamamoto Kansuke and Baba Nobufusa design a new layout. This became the basis of Komoro Castle.^[5]

Historical record

Sengoku Hidehisa turned it into a stone castle

In 1590, after Toyotomi Hideyoshi unified Japan, Sengoku Hidehisa arrived in Komoro as lord of a 50,000-koku domain. He rebuilt the castle on a large scale, adding the second enclosure, the Kuromon gate and the Otemon, and his son Tadamasa built San-no-mon and other gates. Most of the stone walls you see today date from this period. In 1600, Tokugawa Hidetada's army, on its way to attack the Sanada at Ueda Castle, made its headquarters in this castle's second enclosure.^[5][6][13]

Historical record

The Makino family ruled for 170 years

After the Sengoku family moved to Ueda in 1622, the castle changed hands many times and the domain shrank from 50,000 koku. In 1702 Makino Yasushige arrived from Echigo Province, and ten generations of the Makino family ruled from the castle for about 170 years, until the Meiji era.^[5][10]

Historical record

The buildings were sold; two gates survived

In the Meiji era the castle's land and buildings were auctioned off, and most of the palace and gates were dismantled or moved. The Otemon and San-no-mon, however, stayed where they were. The Kuromon gate of the main enclosure was moved to Shogen-in temple in the city, where it still serves as the temple gate. The keep had already burned in a lightning strike in the early Edo period, so only its stone base remains.^[10][12][6]

Historical record

Saved by former retainers, it became Kaikoen Park

Worried that the castle would fall into ruin, former Komoro retainers bought the grounds inside San-no-mon, and in 1880 they built Kaiko Shrine on the site of the main enclosure and named the area Kaikoen, the "park of nostalgia." In 1926 it was redesigned as a modern park by Honda Seiroku, the landscape planner behind Tokyo's Hibiya Park. The Otemon was donated to the city in the Heisei era and restored to its Edo-period appearance.^{[5][10][12][9]}

People of this castle

Had his retainers lay out the castle's original design

Takeda Shingen

武田信玄

1521–1573

A Sengoku-period daimyo of Kai Province (today's Yamanashi) who expanded into Shinano (today's Nagano), taking over and strengthening castles along the way.

First lord of the Komoro domain, who rebuilt it as a stone-walled castle and built the Otemon

Sengoku Hidehisa

仙石秀久

1552–1614

A warlord who served Toyotomi Hideyoshi. He became lord of the 50,000-koku Komoro domain in 1590, rebuilt Komoro Castle as a stone-walled castle, and laid out the town around it.

Lord

Aoyama clan

青山氏

Lord

Tokugawa clan

徳川氏

Lord

Matsudaira clan

松平氏

Lord

Ishikawa clan

石川氏

Lord

Sakai clan

酒井氏

Lord

Takeda clan

武田氏

Lord

Sengoku clan

仙石氏

Timeline

1554
Takeda Shingen takes Komoro and has the castle rebuilt^[5]
1590
Sengoku Hidehisa arrives with a 50,000-koku domain and begins a major rebuilding^[5]
1612
The Otemon is built^[4][14]
1626
The keep burns after a lightning strike and is never rebuilt^[6][15]
1702
Makino Yasushige arrives; the Makino family rules until the Meiji era^[5][10]
1880
Former retainers build Kaiko Shrine in the main enclosure and name the park Kaikoen^[5][10]
1993
The Otemon and San-no-mon are designated Important Cultural Properties^[3][4]

Buildings and remains

The keep today

Keep lost

A three-tiered keep is said to have stood here under Sengoku Hidehisa, but it burned after a lightning strike in 1626 and was never rebuilt. Its stone base survives (the Japan Castle Foundation lists "only the keep base remains").

The site today

The grounds inside San-no-mon are the city-run Kaikoen Park (paid entry), with Kaiko Shrine on the site of the main enclosure, plus a zoo, a small amusement park, an art museum and memorial halls. The Otemon stands in Otemon Park on the other side of Komoro Station; the railway cuts through the former castle. The land of the main enclosure is still owned by descendants of the domain's former retainers.

Main buildings

OriginalImportant Cultural Property

Otemon (main gate)

Built in 1612. Privately used after the Meiji era, donated to the city in the Heisei era and restored to its Edo-period look. The upper floor opens on set days.^[4][8][14]

OriginalImportant Cultural Property

San-no-mon (third gate)

Washed away in the 1742 flood and rebuilt around 1765–66. Its present hipped, tiled roof is thought to date from alterations in the mid-Meiji era. Owned by Kaiko Shrine.^[3][7]

Lost

Keep (tenshu)

Lost to lightning in 1626; only the stone base remains.^[6][15]

Original, relocated

Kuromon (black gate)

The gate to the main enclosure's palace. Moved to Shogen-in temple in the Meiji era, where it serves as the temple gate; its foundation stones remain in the park.^[12][10]

Key facts

Type: Castle
Setting: Hilltop castle (hirayamajiro)built on a low hill rising from the plainEditorial article
Period: Medieval (c.1185–1570s), Early modern (1570s–1871)Editorial article
Keep (tenshu): Keep lostthe castle had a keep, but it no longer stands (its stone base may remain)Editorial article
Built by: Sengoku Hidehisa, Takeda ShingenJapan Castle Foundation
Built: 1554Japan Castle Foundation
Main lords: Aoyama clan, Tokugawa clan, Matsudaira clan, Ishikawa clan, Sakai clan, Takeda clan, Sengoku clanJapan Castle Foundation
Abandoned: 1873Wikipedia (ja)
Remains to see: Gates, Keep base (tenshudai), Stone walls, Moats, Baileys / enclosures (kuruwa)Editorial article
Designation: Important Cultural Properties (Otemon and San-no-mon) (1993); Komoro City Place of Scenic Beauty (Kaikoen Park) (2019)Editorial article
Selection: Japan's 100 Fine Castles No. 26Japan Castle Foundation

Visiting

Access

Open to visitors

Kaikoen Park, inside San-no-mon, needs a ticket (walking ticket or combined ticket). The Otemon is outside the park and open all day. Wheelchairs cannot enter through the Suigetsu ticket gate because of steps at Suigetsu Bridge.

Address

311 Tei, Komoro, Nagano 384-0804 (Kaikoen Park office)^[2][12]

Checked: 2026-10-03

Nearest stations and how to get there

Komoro StationJR Koumi Line, Shinano Railway

about 3 min walk · Not confirmed

Kaikoen Park is a 3-minute walk from the station; the Otemon is on the other (east) side of the station. From the Hokuriku Shinkansen, change at Sakudaira or Karuizawa.^[16][11]

Checked: 2026-10-03

Hours and admission

Kaikoen Park (grounds, museums and more)

Hours: Park 9:00–17:00. Chokokan, the Toson Memorial Museum and the Koyama Keizo Art Museum: April–November 9:00–17:00, December–March 9:00–16:30 (last entry 16:00)
Closed: Open daily through November 30. Closed Wednesdays from December to the second week of March, and December 29 – January 3.
Admission: Walking ticket: 300 yen (high school and up), 100 yen (elementary/junior high). Combined ticket (grounds, zoo, Chokokan, Toson Memorial Museum, Koyama Keizo Art Museum, Komoro Gijuku Memorial Hall): 500 yen / 200 yen (groups of 20+: 400 / 150 yen). Free for preschoolers with a guardian.^[2]

Checked: 2026-10-03

Otemon upper floor (special openings)

Hours: 10:00–15:00 on opening days only
Closed: Opening days for 2026 include weekends and holidays plus October 26–30 in October, and November 1–15 and 21–23 (check the Komoro Tourism Bureau notice).
Admission: Free^[8]

Checked: 2026-10-03

By car / parking

From the Komoro IC on the Joshin-etsu Expressway. Kaikoen parking costs 500 yen for cars, 1,500 yen for large vehicles and 200 yen for motorcycles (per 12 hours). During the autumn-leaf festival (October 24 – November 23, 2026), parking lots 2 and 3 also charge 500 yen per car on weekends and holidays.^[2][16]

Checked: 2026-10-03

Grounds opening hours

9:00–17:00^[2]Checked: 2026-10-03

Time neededEditors' estimate

About an hour to walk around the park; about two hours if you also visit the museums. The Otemon is a few minutes' walk away on the other side of the station.

Steps, slopes and footing

The castle lies below the town, and the grounds are divided by ravines and stone walls, with slopes and stone steps. There are steps at Suigetsu Bridge.^[11][12]

Wheelchairs and strollers

Wheelchairs cannot enter through the Suigetsu ticket gate (steps at Suigetsu Bridge). There are accessible toilets, and an ostomate-friendly toilet next to the Kaikoen Park office.^[12]Checked: 2026-10-03

Toilets and rest

Accessible toilets are at the Sawayaka Fureai-kan rest house, beside the park office, beside the Toson Memorial Museum, at Ohirayama (Baba) and at the children's amusement park. The toilet next to parking lot 2 is out of use. At Ohirayama, apart from the accessible toilet, only squat toilets are available.^[12]

English signs / audio guide

The Komoro Tourism Bureau site has some English headings, but English guide pages and English signage on site are not confirmed.^[11]

Seasons

One of Japan's Top 100 Cherry Blossom Spots. The Cherry Blossom Festival runs in spring (April 1–25 in 2026) and the Autumn Leaves Festival in autumn (October 24 – November 23, 2026).^[11][2]

Photography

Not confirmed. Note that pets are allowed in the park grounds but not in the zoo or amusement park (Komoro Tourism Bureau).^[11]

Works, closures and restrictions

During the autumn-leaf festival, parking lots 2 and 3 charge on weekends and holidays. The Otemon's upper floor opens only on set days.^[2][8]Checked: 2026-10-03

Around the castle

Museum

Toson Memorial Museum

A museum inside Kaikoen Park on the novelist and poet Shimazaki Toson, who taught in Komoro. The building was designed by architect Taniguchi Yoshiro. Entry is included in the park's combined ticket.^[17]

Checked: 2026-10-03

Editors' guide

An editorial guide based on sources and confirmed information — not a first-hand visit report.

Who will enjoy it

Good for people who enjoy how castles use terrain for defense, who are happy to explore stone walls and gates without a keep, or who want to stroll a famous cherry-blossom and autumn-leaf spot. Just three minutes from the station, it also makes an easy side trip from Karuizawa or Sakudaira.

What makes it interesting

Pass through San-no-mon and head for the main enclosure, and you will feel the path going down—the "hole castle" in action. Look for the deep ravine moats, the rough-stone keep base, and the view down to the Chikuma River from the Mizunote lookout at the west end. On the way back, don't miss the Otemon on the other side of the station.

Before you go

Kaikoen Park charges admission and closes on Wednesdays from December to mid-March. The Otemon is in a separate place from the park. The keep burned early in the Edo period, so the two surviving gates are the main buildings to see.

Ways to enjoy it

The park also holds a monument and museum for Shimazaki Toson, so you can combine castles and literature. In autumn-leaf season, the gates are sometimes decorated with lanterns at night.

Photos

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Open questions

The claim that Komoro is Japan's only hole castle comes from the Komoro Tourism Bureau, which says it is "said to be" the only one.
The story that Yamamoto Kansuke designed the castle appears in Komoro City's account but is largely tradition, as is the "mirror stone" he is said to have used.
The three-tiered keep with gold-leaf tiles is described as what "is said" to have existed. The tourism bureau dates the fire to the early Kan'ei era; Wikipedia gives 1626.
The city's statement that Sengoku Tadamasa built San-no-mon and the fact that today's gate dates from around 1765–66 fit together: Tadamasa built the first gate, which was later washed away and rebuilt.
Steps on the route from the station, photo rules inside the museums and English information could not be confirmed. Where the tourism bureau's fee listing differs from the city's, we followed the city.