On the main road between the Runaway and Discovery Bays, Green Grotto Caves is an extensive network of limestone caverns with a subterranean lake and plenty of impressive stalactites and stalagmites. Guided tours take visitors through the history of the caves, which were used by Amerindians as a place of worship and later as a hideout by Spanish troops.

Although it makes a great half-hour trip, the entry fee is rather inflated. There is a pond outside where visitors can fish for tilapia.