William W.
Google
Somewhat touristy, but still a must-do from Rio Tranquilo. There are lots of agencies at the port hawking their tours - it’s CLP$20000 for the “simple” tour to the caves, chapel, and tunnel, and 30000 for the “full” tour (which is about an hour longer and goes across the lake). The tours seem to be available from 7am - 6pm, but strong winds can close the port.
It may be better to visit at sunrise - I did an evening tour and while still pretty, the sun isn’t directly hitting the water. And even though it was a warm day, it was still cool and windy on the boat over. We did see a condor nesting on the cliff face, so keep your eyes peeled!