i did absolve the tomb of anephas quest, no im looking for the way to collasium but i cant find the way to the lost sea.
At the map i see a way west of the skull island, but it is locked with trees. Can anybody help me?

The way to the Lost Sea is THROUGH Anephas' Tomb. The exit to the Lost Sea is the ruined room not far from where you raised Anephas. This was a door that earlier you could find no way to open. Anephas opens it for you.

Hope that helps!

Wyv