Mostly Japanese Mountains: Elephant Mountain and hidden tunnels. Mt. Zo, and the Matsushiro Underground Imperial HQ

S'up, cavedwellers?

I wasn't planning on hiking this day. This was a day I was spending with Mrs. Caveman sightseeing. We decided to go check out the Matsushiro Underground Imperial Headquarters in Nagano City.

Well, as we were walking to the entrance, my caveman's sixth sense started twitching right about here:

What's this? Something caught my attention.

There was a sign marking a trail. A quick look at my hiking app revealed that there was actually a mountain "peak" at the top of the trail. It was Mt. Zo.

Mrs. Caveman is a trooper. She gave me permission to climb the "mountain" after we looked around the cave while she waited in the car. It only took about 20 minutes and the elevation is very low, but my app calls it a peak. Mt. Zo is only 476 meters and is probably the lowest mountain I have ever climbed, but it became my first new mountain of 2026. Although I've been on 10 hikes so far this year, Mt. Zo was my first new one.

. . . about

The Matsushiro Underground Imperial Headquarters is a cave system under Mt. Zo (Elephant Mountain) in Nagano City. This complex, along with two or three other similar locations, was under construction up until the last days of WWII as secure places for the government and military to function. This site is the city of Nagano's official web site for the caves.

Area:

Matsushiro, in Nagano City, has lots of historical sightseeing spots, including the ruins of the Matsushiro Castle and many sites and museums related to the Sanada Clan.