CastleFlatland castle (hirajiro)Next 100 Fine Castles No. 124
What makes this castle distinctive
A castle in the marshes that held out against Ishida Mitsunari's flooding siege and earned the name "Floating Castle"; the three-story turret standing there now was built in 1988, on a new spot, as part of a museum.
Why?
Oshi Castle was built in marshland, and in 1590 it withstood a flooding siege led by Ishida Mitsunari and others, holding out until Odawara Castle surrendered. That story is said to be the origin of its nickname, the "Floating Castle." The castle was dismantled in the Meiji era; the original three-story turret stood near today's Mizushiro Park. The current turret was rebuilt on a different spot in 1988, when the city museum opened.[1][2][5]
The lookout on the fourth floor of the Gosankai Yagura (three-story turret) at the Gyoda City Museum.
What to look at
The views of Gyoda in all four directions, and the displays on the castle and castle town (2nd floor) and modern Gyoda (3rd floor).
Why it's interesting
In the Edo period the three-story turret served as Oshi Castle's symbol in place of a keep. Today's turret was rebuilt in 1988 as part of the museum on the main enclosure site, not on its original spot, and its interior is used for exhibitions. Knowing it is not the original building, compare it with the old maps of the castle town on display.[1][3][4]
Can you see it?
Visible from outsideThe exterior is free to see. To go inside you must enter the museum; the turret cannot be entered directly from outside. Stairs only between floors.
The surviving earthen rampart of the main enclosure
Where
Around the museum, on the main enclosure site.
What to look at
The height of the piled-earth rampart and the trees growing on top.
Why it's interesting
After the castle was dismantled in 1873, very little of the Edo-period castle survived. The museum says part of the main enclosure's earthen rampart, along with dressed kenchi stones used in a turret's stone base, still let you picture the castle as it was.[5][2]
Can you see it?
Visible from outsideFree to see within the park, which is open all day.
03
Mizushiro Park, a remnant of the marsh castle
Where
Mizushiro Park in Gyoda, near where the original three-story turret stood.
What to look at
The broad stretch of water and the park around it.
Why it's interesting
Oshi Castle was built in marshland fed by the Oshi River, using the marshes as its defenses. Mizushiro Park was created from the Oshi Marsh, a surviving part of the castle's moats, and it helps you imagine a castle guarded by water.[6][1][5]
Can you see it?
Visible from outsideOpen as a public park.
At a glance for visitors
Nearest station
15 min walk from Gyodashi Station (Chichibu Railway)
Climb
No climb
Time neededEditors' estimate
About 1.5 hours for the museum, turret and rampart; add 30–60 minutes for Mizushiro Park.
Admission
Adults 200 yen; university and high school students 100 yen; junior high and elementary students 50 yen (groups of 20+: 160/80/40 yen). Free for disability certificate holders plus one carer, among others. Cashless payment accepted.
Hours
9:00–16:30 (last entry 16:00)
Access
Open to visitors
The Oshi Castle ruins park is free and open all day. Entry to the turret requires a museum ticket. The Continued Japan 100 Castles stamp is at the museum during opening hours, and at the Buratto Gyoda tourist and local-products center on museum closing days and from 16:30 to 17:00 (both closed over New Year).
Oshi Castle was built in the late 15th century, in the Muromachi period, by the Narita family, warriors of northern Musashi (today's northern Saitama). It stood in marshland fed by the Oshi River, and the surrounding marshes and water made it hard to attack.[5][7]
02
Historical record
Ishida Mitsunari's flooding siege
In 1590, when Toyotomi Hideyoshi attacked the Hojo clan in the Kanto region, Oshi Castle was besieged by flooding under Ishida Mitsunari and others. The castle held out and surrendered only after Odawara Castle had fallen. It is said that this battle gave it the name "Floating Castle." The museum tells the story with letters from the commanders and a reconstruction drawing of the Ishida Embankment built to flood the castle.[5][2]
03
Historical record
A castle for lords close to the Tokugawa
After Tokugawa Ieyasu took over Edo, Matsudaira Ietada repaired the castle, and then Ieyasu's fourth son, Matsudaira Tadayoshi, became its lord. Under the third shogun, Iemitsu, Matsudaira Nobutsuna and then Abe Tadaaki took charge, and the Abe family held the castle for the next 185 years. In 1823 the (Okudaira) Matsudaira family moved in from Kuwana in Ise Province (today's Mie Prefecture) and ruled until the Meiji era.[5]
04
Historical record
Dismantled in 1873
The castle lost its role in the Meiji era and was dismantled in 1873. The original three-story turret, which stood near today's Mizushiro Park, was torn down at that time. What remains includes part of the main enclosure's earthen rampart around the museum and dressed kenchi stones used in a turret's stone base.[5][1]
05
Historical record
A museum and a rebuilt turret
In 1988 the Gyoda City Museum opened on the main enclosure site, and the three-story turret was rebuilt on a new spot at the same time. On the theme of Gyoda's history and culture, the museum displays ancient haniwa clay figures, materials on the castle town, and Gyoda's tabi (split-toe sock) industry. The castle site is a Saitama Prefecture Designated Historic Spot, and in 2017 it was selected as one of the Continued Japan 100 Castles.[1][5][2][8]
The city museum opens and the three-story turret is rebuilt on a new spot[1][2]
Selected as one of the Continued Japan 100 Castles (stamp available from April 6, 2018)[8][3]
Buildings and remains
The keep today
Modern reconstruction
Edo-period Oshi Castle had a three-story turret instead of a keep. The current turret was "rebuilt on a different site" in 1988 as part of the city museum, in the museum's words. It is reinforced concrete and not on the original spot. The Japan Castle Foundation's list gives no keep for Oshi.
The site today
The main enclosure site is now the Oshi Castle ruins park and the Gyoda City Museum. Part of the moats and marshes survives as Mizushiro Park. The rest of the castle area is now town.
Main buildings
Modern reconstruction
Gosankai Yagura (three-story turret)
The original stood near Mizushiro Park and was lost in the Meiji-era demolition. Rebuilt in 1988 on the main enclosure site; inside are museum galleries and a lookout.[1][5]
Key facts
Type
Castle
Setting
Flatland castle (hirajiro)built on flat ground, defended by moatsEditorial article
Period
Medieval (c.1185–1570s), Early modern (1570s–1871)Editorial article
Keep (tenshu)
Modern reconstructiona keep rebuilt in the 20th century or later; shape or position may differ from the originalEditorial article
Built by
Narita clanJapan Castle Foundation
Built
1479Japan Castle Foundation
Main lords
Matsudaira clan, Narita clanJapan Castle Foundation
Abandoned
1871Wikipedia (ja)
Remains to see
Earthen ramparts, Moats, Gates, Turrets or turret basesEditorial article
Next 100 Fine Castles No. 124Japan Castle Foundation
Visiting
Access
Open to visitors
The Oshi Castle ruins park is free and open all day. Entry to the turret requires a museum ticket. The Continued Japan 100 Castles stamp is at the museum during opening hours, and at the Buratto Gyoda tourist and local-products center on museum closing days and from 16:30 to 17:00 (both closed over New Year).
Address
17-23 Honmaru, Gyoda, Saitama 361-0052 (Gyoda City Museum)[1][3]
Checked: 2026-10-03
Nearest stations and how to get there
Gyodashi Station (Chichibu Railway)Chichibu Railway Chichibu Main Line
about 15 min walk · No climb
About 15 minutes on foot through flat town streets.[5][2]
Checked: 2026-10-03
JR Gyoda Station (by bus)JR Takasaki Line
No climb
Take the city loop bus (West Loop, clockwise) to Oshijoshi Kyodo Hakubutsukan-mae, right by the museum (about 23 minutes). From JR Fukiage Station, take an Asahi Bus to Oshijo stop.[5][2]
Checked: 2026-10-03
Hours and admission
Gyoda City Museum (including the Gosankai Yagura)
Hours
9:00–16:30 (last entry 16:00)
Closed
Mondays (open on holidays), the day after a holiday (open if it falls on a weekend), the fourth Friday of each month (open during special exhibitions), New Year holidays, and occasional closures
Admission
Adults 200 yen; university and high school students 100 yen; junior high and elementary students 50 yen (groups of 20+: 160/80/40 yen). Free for disability certificate holders plus one carer, among others. Cashless payment accepted.[3][10][2]
Checked: 2026-10-03
By car / parking
Free museum parking: Lot 1 (4 buses, 33 cars; buses must reserve) and Lot 2 (23 cars plus 1 accessible space). Entrance on Prefectural Road 128.[9][5]
Checked: 2026-10-03
Grounds opening hours
The castle park is open all day (free).[2]Checked: 2026-10-03
Time neededEditors' estimate
About 1.5 hours for the museum, turret and rampart; add 30–60 minutes for Mizushiro Park.
Steps, slopes and footing
A flat site with almost no slopes. Inside the turret there are stairs only.[1]
Wheelchairs and strollers
The turret has stairs only. One accessible parking space. Other accessibility features inside the museum are not confirmed.[1][5]Checked: 2026-10-03
Toilets and rest
Not confirmed
English signs / audio guide
No English information could be confirmed.
Seasons
Not confirmed
Photography
Photos are allowed in the galleries except for items marked otherwise. No flash, tripods or selfie sticks, and no video. Photos are for non-commercial use.[11]
Works, closures and restrictions
No eating or drinking inside. Fresh flowers, wet umbrellas and pets (except assistance dogs) may not be brought in.[12]Checked: 2026-10-03
A park created from the Oshi Marsh, part of the castle's old moats. The original three-story turret stood near here.[6][1]
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 anyone interested in the famous flooding siege of Oshi Castle, and for those who like to learn a castle town's history in depth at a museum. Admission is inexpensive and the site is easy to see in a short visit.
What makes it interesting
The turret is a 1988 rebuild on a different spot. The genuine traces are the main enclosure's earthen rampart and Mizushiro Park, a remnant of the moats. See the museum's displays on the siege and the Ishida Embankment first, then step outside and picture a castle surrounded by marsh.
Before you go
The turret is joined to the museum and cannot be entered on its own from outside. The museum often closes on Mondays, the day after holidays and the fourth Friday, so check the calendar before you go.
Ways to enjoy it
After looking out over the town from the lookout, walk along the main enclosure's rampart and, if you have time, head to Mizushiro Park. Gyoda is also a tabi-making town, so don't miss the museum's display on tabi and Gyoda.
Photos
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Open questions
The idea that the name "Floating Castle" comes from surviving the flooding siege is a tradition.
Today's turret is reinforced concrete and on a different spot from the original. The official sources do not say how closely its exterior matches the original; Wikipedia says its position and size differ from the historical turret.
The year of the prefectural designation, toilets, accessibility features inside the museum, and English information could not be confirmed.
Saigen JiroCC0Wikimedia Commons
