How do I get inside the monastery?

Hint 1 of 10:

You'll need help from someone.

Hint 2 of 10:

Dead souls can be quite helpful.

Hint 3 of 10:

Wear the Ring of Water to get the Will-of-th'Wisps to appear.

Hint 4 of 10:

Then, talk to them and ask them to bring the boat.