Bottomless Lake is an Ainigmata Ostraka found in Kephallonia Island of the game Assassin’s Creed Odyssey.
You can find this tablet at the bottom of the water at Melissani Cave before you actually enter the cave for the quest In the Footsteps of Gods.
Bottomless Lake
GREECE – Kephallonia
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.
Ironically, since you find it at the bottom of a pool of water, you’ll also find the final piece of it to a larger bowl of water to the south. It’s not at the bottom, but on the ledge of a side portion, where a statue is.
Don’t forget to use Ikaros at the larger basin, because there are a lot of Treasures beneath it, not all of them at the bottom, either.