Dive into the depths of Kaiyama Underground Bunker, a hidden stronghold built by the Yokosuka Naval Air Corps during World War II. Partially open to the public, this site also hosts rare tours. Let’s delve deeper into this historical legacy.

Preserved history since 1944: Kaiyama Underground Bunker

The Kaiyama Underground Bunker, located in Oppamacho, Yokosuka City, was a major stronghold constructed by the Yokosuka Naval Air Corps. Excavation of this extensive underground complex, spanning approximately 2 kilometers, commenced around 1944 towards the end of the Pacific War. Situated beneath the Kaiyama Green Park, parts of it have been open to the public since 2021.

The Kaiyama Underground Bunker features numerous entrances across the mountain, dividing it into northern and southern sections. The northern part primarily served as the headquarters, boasting lengthy main tunnels that connected various chambers. Conversely, the southern section comprises large interconnected rooms utilized for the storage of supplies and weapons.

Moreover, there are separate linked bunker and fuel storage facilities, earning it recognition as one of Japan’s premier naval underground bunkers due to its scale and structure.

Guided Tour: Kaiyama Underground Bunker

Experience a monthly tour where you can immerse yourself in the deep history of the Kaiyama Bunker.
Don’t miss out on this rare opportunity to explore its secrets firsthand.

Kaiyama Underground Bunker Tour Official Web page (JP)
Yokosuka Tourist Information Web page (JP)
Yokosuka Route Museum Web page (EN)

Date and Time

Date: Every 2nd Saturday of the month

Time: 10:00 AM to 12:30 PM

Kaiyama Underground Bunker Calendar (JP)

Registration

Registration Link down below

Kaiyama Underground Bunker Official Registration Link

– Up to 6 participants per registration (1 person or more).
– Participants must be middle school age or older and capable of independent walking.

Registration Deadline and Fee

– Registration must be completed by the Friday two weeks before the tour date.
– Tours exceeding capacity will be closed for registration.
– ¥700 per person, payment accepted on sight.

Tour Course: Walking through the History

1. 3rd Naval Fort Remnants (Meeting Point)

2. Explore inside the Kaiyama Underground Bunker

3. Fuel Storage Tanks at Oppama Purification Center

4. Kaiyama Green Space

5. Monument of the Birthplace of Naval Preparatory School

6. Monument of the Birthplace of Naval Aviation

7. Flight Preparatory Trainees Memorial Monument

8. Kaiyama Green Space Observatory

9. Oppama Shako-mae Bus Stop (Goal)

Total: Approximately 3 km

How to Access

From Keikyu Line’s “Oppama” Station, there are various transportation options available for accessing the Kaiyama underground bunker.

On Foot	Approximately 30 minutes
Bus	From Keikyu Bus Stop “Oppama Station Front” ［Bus Route 1］ Bound for “Oppama Shako-mae” → Take off at “Oppama Shako-mae” → Approximately 5 minutes on foot ［Bus Route 2］ Bound for “Fukaura via Taura” → Take off at “Tokyo Fine-mae” → Approximately 10 minutes on foot
Taxi	Approximately 5 minutes
Car	Paid parking available in front of the Third Seawall ruins

Requirements

1. Maximum of 30 participants. In case of exceeding capacity, registrations will be processed on a first-come, first-served basis. (Confirmation of participation will be sent to the representative after the deadline)

2. Tours require a minimum of 6 participants to proceed. Tours will be canceled if the minimum is not met.

3. Tours proceed with rain but there is a chance that will be canceled in severe weather conditions.

Additional Information

1. Participants will be enrolled in accident insurance, included in the participation fee.
2. Details regarding tour precautions and necessary items will be provided in the participation guide on the day of the tour.

For cancellations or inquiries after registration or after the deadline, please contact the following email address.
ycg@kankoh-guide.com

Afternote

This tour offers a rare opportunity to explore Yokosuka City’s history and culture while delving into the mysteries and history of the Kaiyama Underground Bunker. Embark on this valuable experience guided by local experts, and uncover the secrets of this facility aimed at subterraneanizing the air corps.