What's the basic idea here?

Hint 1 of 9:

Have you used your binoculars to look at the tower?

Hint 2 of 9:

Then you know that the vase you've been looking for can be found there.

Hint 3 of 9:

So you're trying to get to the tower -- at all costs.

Hint 4 of 9:

Unfortunately, you can't walk or fly across.

Hint 5 of 9:

So you'll have to try floating across.

Hint 6 of 9:

But that means you need to find a way to get the city underwater.