The Green Grotto Caves are show caves and a prominent tourist attraction on the north coast of Jamaica. Named for the green algae that cover its walls, the structure of the cave is strikingly different from inland systems; the cave is a Flank Margin Cave (old mixing chambers at the edge of the fresh water lens with the sea water) with two well-defined levels apparently indicating two periods with differing sea-levels. The innermost cavern contains a crystal-clear underground lake.