CastleMountain castle (yamajiro)Next 100 Fine Castles No. 119
What makes this castle distinctive
On the slopes of rock-faced Mount Iwabitsu stands the castle where Sanada Masayuki is said to have built a residence in just three days to receive his fleeing lord, Takeda Katsuyori.
Why?
In 1582, as Oda and Tokugawa armies closed in on Takeda Katsuyori, Sanada Masayuki urged him to regroup at Iwabitsu. According to the town, Masayuki rushed back and had a residence for Katsuyori built at the southern foot of the mountain in three days. But Katsuyori never came; he took his own life at Mount Tenmoku. The residence site survives as Senryuin-ato.[2]
The honmaru site at 593 m elevation, reached by the Onedori (ridge) trail from the Hirasawa trailhead.
What to look at
The long, narrow main enclosure (about 140 m east–west and 35 m north–south) and a raised platform about 25 m by 15 m that appears to be a building base.
Why it's interesting
The platform is thought to mark the castle's nerve center, combining a lookout and command post. Enclosures (kuruwa) spread along four ridges running east from the honmaru, and the town describes the castle as one of the largest medieval castles in Gunma Prefecture.[2][3]
Can you see it?
Visible from outsideReached on foot by mountain trail. Climbing is discouraged in winter (December–March).
A wide tatebori (a moat dug straight down the slope) and another moat that bends at a right angle.
Why it's interesting
Vertical moats stop attackers from moving sideways across a slope, and the town notes that adding a bend made them even more effective. No buildings survive, but moats and enclosures like these remain much as they were, one reason the site became a National Historic Site.[2]
Can you see it?
Visible from outsideVisible from the trail.
03
Senryuin-ato, the residence built for Takeda Katsuyori
Where
On the south side of Mount Iwabitsu, near the Akaiwa trailhead.
What to look at
Stone walls on a grassy terrace, with the rock face of Mount Iwabitsu rising behind.
Why it's interesting
This is said to be the site of the residence Sanada Masayuki built in three days to receive Takeda Katsuyori. Katsuyori died without ever coming, and the building was kept by the Nezu family, relatives of the Sanada, as Senryuin until the Meiji era. In 1884, the town says, its goma hall became the main hall of Kentokuji temple in Haramachi.[2][3]
Can you see it?
Visible from outsideNear the start of the Akaiwa trail.
At a glance for visitors
Nearest station
40 min walk from JR Gumma-Haramachi Station
Climb
Steep climb
Time neededEditors' estimate
About an hour for a round trip from the Hirasawa trailhead to the honmaru site; allow 2–2.5 hours to include the summit, as on the town's map.
Admission
Free
Hours
9:00–16:00 (April–November)
Access
Open to visitors
The castle site is reached only on foot by mountain trail, and climbing is discouraged from December 1 to March 31. The Next 100 Castles stamp is at the Hirasawa Trailhead Tourist Information Center from April 1 to November 30 (9:00–16:00) and at the Higashiagatsuma Town Tourism Association from December 1 to March 31 (9:00–17:00). It is unavailable over the New Year holidays.
Iwabitsu is a mountain castle (yamajiro) on the eastern slopes of Mount Iwabitsu (802.6 m), whose southern face is a cliff about 200 m high. Its main, second and middle enclosures sit some 200 m below the summit, and the valley of the Kirisawa stream, the lower slopes and the Agatsuma River are thought to have served as natural moats. Its layout is large and complex, taking in even the castle town.[2][4][1]
02
Historical record
Origins unknown; first lord Agatsuma Taro
When and by whom the castle was built is unknown, but it is believed to date from the medieval period. The first lord on record is Agatsuma Taro Yukimori, in the Nanboku-cho period (1336–1392). In the Sengoku period the Saito clan ruled the eastern Agatsuma area from here.[2][3]
03
Historical record
Taken for the Takeda by Sanada Yukitsuna
In 1563 Sanada Yukitsuna (Yukitaka), acting on orders from Takeda Shingen, attacked Iwabitsu. Its lord, Saito Norihiro, made the most of the rugged castle, but it finally fell. The area then came under the Takeda and later the Sanada, and Iwabitsu became a key midway base on the Sanada road linking Ueda and Numata castles.[2][3]
04
Tradition
The refuge offered to Katsuyori
In 1582, with Oda and Tokugawa forces attacking Takeda Katsuyori, Sanada Masayuki is said to have urged him to make a comeback at Iwabitsu and hurriedly built a residence to receive him. Katsuyori never reached Iwabitsu and died at Mount Tenmoku, and the castle is remembered as a place that might have changed history had he come.[2]
05
Historical record
Destroyed under the one-castle rule
After the Hojo fell in 1590, Masayuki's eldest son Nobuyuki became lord of Numata, and Iwabitsu served as a branch castle governing Agatsuma District. It stayed on Nobuyuki's side after the Battle of Sekigahara (1600), but in 1615 it was demolished under the shogunate's one-castle-per-province rule. No buildings remain, but the enclosures and moats are well preserved.[2][3]
06
Historical record
A National Historic Site since 2019
On October 16, 2019, the Iwabitsu Castle ruins became a National Historic Site covering about 21 hectares. The national listing calls it a border castle contested by the Takeda, Hojo and Uesugi, whose large, complex layout including its castle town is extremely important for understanding the Sengoku period in eastern Japan.[1][2]
Selected as No. 117 of the Next 100 Fine Castles of Japan[8]
Designated a National Historic Site (about 21 ha)[1][2]
Buildings and remains
The keep today
No keep was built
A Sengoku-period mountain castle with no keep (the Japan Castle Foundation lists none).
The site today
Enclosures and moats survive in the forest on the mountainside; there are no buildings. Hiking trails run through the castle site and on to the summit.
Main buildings
Key facts
Type
Castle
Setting
Mountain castle (yamajiro)built on a mountain; expect a climbEditorial article
Period
Medieval (c.1185–1570s), Early modern (1570s–1871)Editorial article
Keep (tenshu)
No keep was builtthe castle never had a keepEditorial article
Main lords
Sanada Masayuki, Sanada Nobuyuki, Takeda clan, Saitō clan, Sanada clan, Sanada YukitakaJapan Castle Foundation
National Historic Site (Iwabitsu Castle ruins) (2019)Editorial article
Selection
Next 100 Fine Castles No. 119Japan Castle Foundation
Visiting
Access
Open to visitors
The castle site is reached only on foot by mountain trail, and climbing is discouraged from December 1 to March 31. The Next 100 Castles stamp is at the Hirasawa Trailhead Tourist Information Center from April 1 to November 30 (9:00–16:00) and at the Higashiagatsuma Town Tourism Association from December 1 to March 31 (9:00–17:00). It is unavailable over the New Year holidays.
About 40 minutes on foot (uphill) or about 10 minutes by taxi to the Hirasawa trailhead. There are no buses and no taxis waiting at the station. From the trailhead you continue on a mountain trail.[5][6]
Checked: 2026-10-03
Hours and admission
Iwabitsu-yama Hirasawa Trailhead Tourist Information Center
About 50 minutes from the Shibukawa-Ikaho exit of the Kan-Etsu Expressway. The Hirasawa trailhead has parking for 70 vehicles (large vehicles OK) and toilets.[4][6]
Checked: 2026-10-03
Grounds opening hours
No set hours confirmed; climbing discouraged December 1–March 31[7]Checked: 2026-10-03
Time neededEditors' estimate
About an hour for a round trip from the Hirasawa trailhead to the honmaru site; allow 2–2.5 hours to include the summit, as on the town's map.
Steps, slopes and footing
The castle site is reached on dirt mountain trails, with several routes such as the ridge trail (Onedori) and the gully trail (Sawadori). The summit route has chains, bare rock and ladders; the town recommends proper hiking clothes and trekking shoes or boots. Use the detour around Tengu-no-Kakehashi (Goblin's Bridge). Southern trails also start from JR Gobara Station, which is unstaffed.[4][5]
Wheelchairs and strollers
The mountain trails are not suitable for wheelchairs (no official accessibility information confirmed).Checked: 2026-10-03
An autumn-leaves festival is held at the Hirasawa trailhead every November 3. Fresh spring green and autumn color are popular seasons for hikers.[5][4]
Photography
Not confirmed
Works, closures and restrictions
Climbing is discouraged from December 1 to March 31. The Hirasawa information center is closed during that time and the stamp moves to the Higashiagatsuma Town Tourism Association.[7][9]Checked: 2026-10-03
Suggested routes
Mount Iwabitsu round trip (about 2 hours) 120 min
From the Hirasawa trailhead (parking, information center) to the Onedori junction
From the honmaru junction, follow the Sawadori trail to Hitsu-no-kuchi and the ninth station
Climb past the chain sections to the summit of Mount Iwabitsu (802.6 m)
Return to the ninth station and Hitsu-no-kuchi, then take the Onedori trail
Visit the Iwabitsu Castle honmaru site via the Akaiwa-dori junction
Return to the Hirasawa trailhead via the Onedori junction
A recommended course from Higashiagatsuma Town's guide map (difficulty two stars out of three). There are chains and rock near the summit; take the detour around Tengu-no-Kakehashi. Climbing is discouraged December–March.
Castle site and Mount Iwabitsu (about 2.5 hours) 150 min
From the Hirasawa trailhead via the Onedori junction to the honmaru site
From the Akaiwa-dori junction descend the Junisama-dori trail to the Gobara Castle site and Senryuin-ato
Continue via the Furuya T-junction to the Mitsuiwa trailhead
Climb the Mitsuiwa-dori trail past the saddle, the Tengu-no-Kakehashi detour and the Takanosu rock-shelter site to the summit
Descend via the ninth station and Hitsu-no-kuchi on the Sawadori trail to the honmaru junction
Return to the Hirasawa trailhead via the Onedori junction
A recommended course from the town's guide map (difficulty three stars out of three). The Mitsuiwa-dori trail is the most demanding route, for experienced hikers, with chains and rock scrambles.
Editors' guide
An editorial guide based on sources and confirmed information — not a first-hand visit report.
Who will enjoy it
Good for hikers who want to see the moats and enclosures of a Sengoku mountain castle, and for fans of Sanada history. The summit, with its chain sections, is for those used to such climbs.
What makes it interesting
The broad honmaru with its building platform, and the long vertical moat below it. If time allows, visit Senryuin-ato on the south side and recall the story of the welcome prepared for Katsuyori.
Before you go
The castle site is in the mountains and has no buildings. Climbing is discouraged in winter (December–March). There are no buses from the station and no taxis waiting there, so plan your return trip. Wear proper shoes and clothing.
Ways to enjoy it
Pick up a map and pamphlets at the Hirasawa information center before you set off. The mountain is colorful around the November 3 autumn festival. Iwabitsu lay midway on the Sanada road between Ueda and Numata, so combining it with Nagurumi and Numata shows how far Sanada power reached.
Photos
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Open questions
When and by whom the castle was built is unknown. The tale of Agatsuma Taro Yukimori's fall and the story of a residence built for Katsuyori in three days are presented as legend even in the town's materials.
That it is among the largest medieval castles in Gunma and one of the three great castles of the Takeda domain are claims made by Higashiagatsuma Town.
Official materials give only segment times, not a single figure, for the walk from the Hirasawa trailhead to the honmaru site. English information, photo rules and accessibility details were not confirmed.
Koda6029CC BY-SA 4.0Wikimedia Commons
