Very interesting caves in which you can face some of your fears. The entrance of the cave has some nice light effects as the sun breaks in through some holes in the ceiling (the sun needs to stand high in the sky). But the actual highlight are the other parts which lead further into the mountain, and where you can find millions of bats hanging from the ceiling and millions of cockroaches cover the walls and the floor. Walking deep enough into the cave it is also possible to find some pythons hiding in rock niches.
There're some adventure packages on offer, including a guide but quite expensive (see picture).
If you go by yourself bring a headlamp and grab one of the umbrellas lying underneath the entrance stairs. The entrance fee seems a bit expensive but can be negotiable (50.000 IDR/person in my case; foreigners pay more than locals).