is there a way to go back to Sentinel island after Battle tower? spoiler.

[Trespasser07]

I need to complete the quest w/ the ship atop a tree.

[Raze_Larian]

Yes (one of the teleporter shrines will remain active). Everything else on Sentinel Island should be completed, but you can return outside after taking over the battle tower (and must to complete that quest; there is also some additional loot available).
The same is true for Broken Valley; do everything you want to do before taking over the battle tower, but the quarry tower will remain locked until after that point.

[Trespasser07]

Originally posted by Raze_Larian:

Yes (one of the teleporter shrines will remain active). Everything else on Sentinel Island should be completed, but you can return outside after taking over the battle tower (and must to complete that quest; there is also some additional loot available).
The same is true for Broken Valley; do everything you want to do before taking over the battle tower, but the quarry tower will remain locked until after that point.

Thanks, was able to fly to that ship by the tree. But everything else on the island was pretty much fogged out.

[Raze_Larian]

There are a couple treasure chests in wyvern nests, etc, you can transform above to drop into.
If you fly away from the island, the poison fog will thin out and disappear, but there isn't too much of note. Other than loot, there is something you can find if you fly in the direction of the fjords, north east of the island: hint check rocks sticking out of the water and you can find (spoiler)Michael's raft (the guy planning to escape the island in the shipwreck camp), just off the eastern edge of the map, north of the broken ship on columns sticking out of the water (where you can find more loot, and a book).

BTW, you may want to read the book from the ship in the tree yourself, rather than return it to complete the quest (you can not do both; the NPC will be annoyed if you talk to him again, but you don't need to do so, and he isn't involved in anything else).