Five miles of underground river link lake to ocean.

An island in the middle of a lake, in the middle of a volcano, in the middle of a bigger lake, in the middle of a bigger island, in an archipelago, in the Pacific Ocean.

This holy site either displays a centuries-old cross or a complete fake.

The ruins on a deserted tropical island in the Philippines bear the scars of WWII.

Holy Hindu shrine in an enormous, monkey-filled limestone cavern.