What is the ship icon near Ysgramor's Tomb?

On my way to Ysgramor's Tomb, I saw a ship outline to the northwest and went to investigate. I went out into the ice flows and the ship outline on the compass began to highlight as I got closer. Then, it went poof and disappeared. I never was notified that I arrived some place, and it does not show up on my map. Does anyone know what this ship is and how do I reach it?


It is an under water ship, which can be investigated, if you want to investigate fully i recommend either a water breathing potion or spell.


Sounds like Pilgrim's Trench