San Sebastian de la Grutas is a small town (en route to Puerto Escondido) famous for its explorable caves. The caves have many different paths and arms to walk around in. The guides there are excellent and the best moment is when everyone turns their lights off and you find yourself in pure darkness.
This spot makes for a great day trip out of Oaxaca (or you could stop by on your way to the coast).
Thanks to Johanna Palmieri for sharing her awesome pictures for this page!
Busses to San Sebastian de las Grutas leave from the corner of Mier y Teran and Mina. The bus line is called San Pedro el Alto and these busses go from 4am to 6pm. It takes about 2 hours to get to the town, where you can stay in their comfy cabins.