When exploring The Nameless Isle, you should encounter the entrance to the Temple Of Vrogir. It will turn out that it's flooded. You have to solve this inconvenience.
The solution lies in the nearby Black Ring camp. You will find there the Portalmaster, who maintains the portal on water. There are two possibilities:
Choice 1: peaceful
If you haven't sided with the magisters, you can claim that you're a Lone Wolf, which will let you freely enter the camp. Talk to the Black Ring Captain when you're there and ask him to move the camp. If your persuasion is high enough, you will be able to convince him to move out.
Reward: 50150 experience points
Choice 2: combat
If your persuasion isn't high enough, though, or you have sided with the magisters, you will have to kill the Portalmaster along with the rest of the men in the camp...
Reward: 210 650 experience points