u/Pharap

The Hundred Caves of Yoshimi are a series of tombs dug into artificial caves in a tuff (volcanic rock) cliff in Saitama, in the Kanto region of Japan.

The pictured tunnels are very close to how I imagined the tunnels of D'ni being when reading The Book of Atrus.

The outside is also very unusual, as it resembles a large termite mound, which is definitely the kind of thing I'd expect to see in some other age.