The location is a slate mine in the Sauerland, Germany. It lies at the bottom of a large slate dump right at the River Ruhr and has a long history. For further information check out:
http://www.bergwerktauchen.de
Since I'm a diver I always had this dream to dive with Whale Sharks. 9 years ago I wanted to fulfill this dream, but in my time frame for vacation it wasn't the season in Australia so I traveled to Mexico instead.
Making of the first Cave Diving Flash Mob + Bonus Material
"A lot of people asked us how we made this cave diving flash mob so let us give you some insights about the whole experience and as well why Steve wasn't really alone at the end ;)"
Cheers
HP