I have tried the Atlantis Submarine in St. Thomas. They offer the same excursion in GC as well as a more personal sub (much more expensive). The submarine holds about 44 people and if you are claustraphobic it may be intimidating for you. You must climb through a hole to get into the sub, then you are seated arm to arm with the other people on the trip. Once inside the area felt very open. We were lucky though and didn't have anyone sitting on either side of us, not that it would have mattered much. Your view is out of a porthole in the side that your seat faces. You do not really feel any motion as you under the waves. It was really an incredible time and my DS6 absolutely loved it. I am glad we decided to cancel my DW as I don't think she would have ended up going in. It does look tight when you are climbing down. I think the semi-sub has an even more "open" feeling to it. The Atlantis is an actual submarine. We went about 85 feet under the water on our trip, but we got to see sharks, barracuda, turtles, lobster, some ship wreck parts, many beautiful fish, it was a really great experience. You just need to know your tolerance for confined spaces.