Not really a cave, this was actually taken at an old Spanish fortress in Brazil on a river boarder with Bolivia. The walls were alive with the chirps of bats. There must have been millions of them, every crack was filled with them.

I haven’t identified what kind of bat this is yet so any ID help is welcome.

Nikon D80
Tamron 70-300mm
1/125s
f/5.6
ISO 100
Flash SB-600
June 2011