So, I enter this instance, and did this several times, to make sure.
And I am below the floor, with furniture and decorations floating above me and my companions and enemies -- and darkness under me and everyone else and all around us. When the fight starts, all you can see of everyone is the tops of heads thru' the floor.
And the exit seems to be disabled, so no backing out normally. To get out, I had to port to the nearest Life Fountain each time and run/sail back.
Obviously, there's no playing this area until this is fixed. First time so far I've seen a graphics glitch this bad in this game. Other times have been in communal areas where a log-out/long-in fixed it.
You didn't mention what area this was, what quest you are on, or what level or class your Pirate is so it is very hard to help you. When I had trouble with floating in the Skyway, Support found that I needed to update my video drivers. This sounds like it could be the same type of problem. If that is not it, use the Help Menu above (the Orange Question Mark) to contact Support and I am sure that they can help you.