We did the Seaworld Explorer in Curacao. From the surface, it is a flat decked boat, looks a lot like a barge. There are two hatches, fore and aft (front and back). You walk into the rear hatch and down the steps, into the hull. The hull is a deep V shape, maybe 7foot of height, so no stooping required. The the bottom of the hull is only about 4 feet across and there are metal seats folded up against the side. You go in two by tow (like Noah) and fill it front to back. When everyone is in, you put the seat down and sit. There are huge windows along the entire length, both sides. You are roughly 8 to 10 feet below the surface. If kids get scared or someone panics, they can get out, but it is not easy, you need to climb over a few people to do so. There is no room to walk around.
That said it was pretty cool. Although I think next time my wife wants to do the Altantis submarine. I like to actually be in the water (diving or snorkeling) so I will probalbly skip it.
The underwater life in Aruba is some of the best, so if you are not into getting wet yourself, I would suggest this or the submarine.
