This is the Mutsuura Ammo Factory used by Japan during World War II. A military bunker located in the Kanagawa Prefecture in the Kanto Region of Japan. Carved out through muddy tunnels this is truly a relic, found only by a whole that cut down into the ground and led into tunnels filled with Mukade, a large centipede.
For now it is mostly left alone except for visits from the wandering adventurer.
Photographed by Jordy Meow