4 swimmers entered a round room with no windows and no doors, but there was a hole in the floor.
One man left through the hole in the floor and closed it behind him, but it is not how he arrived.
2 others were also found in the interior room, which had electricity and lighting, but a third was found dangling from his feet from the ceiling, with a puddle of water on the ceiling above him.
3 days later, the first swimmer was found floating face down in the hole in the floor, since it wasn't actually an exit, but actually an entrance to a system of caves with a lake inside it.
How did everyone actually enter the room, and who killed the swimmer in the cave?