While continuing my island-hopping around the Tokyo area, I learned that there’s a normally off-limits artificial island in Tokyo Bay. Daini Kaiho (Second Sea Fort) — an artificial island off the coast of Futtsu, Chiba Prefecture, built in the Meiji era as a maritime fortress for the defense of Tokyo Bay. In recent years, limited tours have made landing possible.

Access

Daini Kaiho cannot be visited individually. You must join a tour organized by a travel company. All tours are conducted in cooperation with the Tokyo Bay Kaiho Tourism Organization, with a dedicated guide accompanying each landing. A signed pledge is required on the day.

Major tour operators include:

  • Hato Bus: Day trip from Tokyo Station. Includes Mikasa warship visit and navy curry lunch.
  • Club Tourism: Solo traveler plans and two-island tours (with Sarushima).
  • Lawson Entertainment (Iore): Combined tour with Sarushima.
  • Nitto Kotsu: Cruise-style tour departing from Futtsu Port.

All operators run tours on irregular dates, subject to cancellation due to weather or sea conditions. Check the latest tour schedule on the Tokyo Bay Kaiho Tourism Organization website.

Tour Details

I joined a Hato Bus day tour (Course No. R7757).

  • Price: ¥17,800 per adult (tax included; lunch, boat, and admission included)
  • Meeting point: Tokyo Station Marunouchi South Exit, departing 9:30
  • Return: Tokyo Station, arriving approximately 17:20
  • Schedule: Irregular dates only. Minimum 20 participants required.
  • Organizer: Hato Bus (in cooperation with the Daini Kaiho Landing Tourism Promotion Council and the Tokyo Bay Kaiho Tourism Organization)

Tours may be canceled on the day due to weather or sea conditions.

The price is not cheap for a day trip, but there is no other way to land on Daini Kaiho. For someone working through an island-hopping list, it was a necessary expense.

Itinerary

09:30 – 11:00Tokyo Station → Yokosuka Hato Bus
11:00 – 12:10Lunch Yokosuka Navy Curry Honpo Bayside Kitchen
13:00 – 13:30Yokosuka Port → Daini Kaiho Boat
13:30 – 14:30Daini Kaiho landing and tour Guided
14:30 – 15:00Daini Kaiho → Yokosuka Port Return
15:00 – 15:40Memorial Ship Mikasa Mikasa Park
16:00 – 17:20Yokosuka → Tokyo Station Hato Bus

Daini Kaiho

Tokyo Bay has three kaiho (sea forts): First, Second, and Third. Construction of Daini Kaiho began in 1881 and took about 25 years. It was a military stronghold with gun emplacements and ammunition storage, decommissioned after World War II. It remained off-limits under the Ministry of Land, Infrastructure, Transport and Tourism until limited tours were permitted in the 2020s.

After landing, a guide led a roughly one-hour walk around the island. Gun emplacements, ammunition bunkers, and observation facilities remain. From the island, numerous cargo ships and naval vessels could be seen passing through Tokyo Bay, making it easy to understand why this location was chosen as a fortress.

Important note: there are no restrooms on Daini Kaiho. Use the facilities before boarding the boat.

Why I Chose This Tour

While continuing my island-hopping around Tokyo, I learned about tours that allow landing on this normally restricted site. Daini Kaiho is inaccessible without a tour. Tour dates are limited and subject to weather cancellation, so I applied as soon as a date was available.