I'm trying to find a book I read between 1994 and 1998. I read it in French, and have no idea if it has been written / translated in English.
The book started with three young friends going camping alone next to a lake. While scuba diving in the lake, they find a cave from which they travel to another world (maybe a parallel universe). Then the rest of the book has them trying to find a way back to their world.
Also I can remember one of the final twists in the end of the book, if that can help find it:
The "master of the universe" happens to be one of the two or three young campers from the very begining of the book. And IIRC he wears glasses.
