.hack//G.U. vol. 3//Redemption

You can go when you get an e-mail about the ceremony asking you to come to Hy Brasail, but it's a one time chance and you lose it once you've talked to Taihaku after the tournament. It's one of, if not the only limited time opportunity you have to deal with in G.U.. A lot of players miss this and don't even know it (just look at the answers you've gotten so far for proof) because they go straight to the Icolo @HOME instead, after which a down for maintenance e-mail appears signaling that your chance is gone.

If you do happen to miss it and can't be bothered to replay the game to see it, I have probably the only movie of what happens there online:

http://www.youtube.com/watch?v=4WX9teWaqD8

Afterward, you can go back to town after talking to the captain, but like in past games, you can explore the island for as long as you want before you go.

Also, while the marriage ceremony does take place there, you only see the island in pictures; you don't actually visit it, so that's not the answer you're looking for.