KEPHALLONIA ISLANDS | Melissani Cave
Riddle Name: Bottomless Lake
"Taking the plunge? Everyone on the island thinks this is the deepest dive, but there is a lake in the Coast of Koliadai that is rumored to be bottomless. If you are able to dive as far as the woman in marble, you will be able to claim me."
At the bottom of the lake, where you jump in at the Melissani Cave. Next to the Loot Treasure.