So I lifted the curse from the island and the follow ups but there is a door to the tower with an entrance from outside and first floor inside. I have not found a way to open it. Can it be opened?

Shameless bump

i never found a way to open it either :(

Any time I find a locked door, I assume some quest somewhere will unlock it for me.

Another example... I'm on a quest to go to some building. The building has two entrances that are normally both open. During the quest, the one door is locked because there is a cutscene waiting for me at the other door.