[Ellipsis]

@ R4x0r: I thought about this too. Ship captains won't take you there (there is no such option) but in order to go to Thanatos you need to get your own boat. However, Razors Pointe was not a travelling option as well after getting said boat...

@ Jimwth: Thank you for the suggestion! =) The walkthrough said: "if you journey back to Blackroot, and from there head SW towards Caladon and go as far along the coast as it it possible to go, you come to a place called Razors Pointe (1504 W, 1772 S). There are two shipwrecks there. If you make your way along the path that runs through shallow water, you'll find a lot of Barrels and Chests. Unfortunately, you also find Aria's body on the deck of the second ship".
It sounds a lot like what I did (marking a nearby point and then following the coast...), but maybe I missed something. I'll try it again and post about it later.