unforgettable team-building

What is one team-building activity at your workplace you will still remember after 10 years? 

For me, it was one activity invented by my team, which I'll call "Remote Control". It is a team vs team race game. Each team has one blindfolded person assigned to hunt treasures. He has a camera mounted on his face, to allow his teammates (in another room) to see his surroundings. He can only hear instructions and cannot speak. His teammates need to guide him from a remote location to find all treasures. Sounds simple, but very challenging in practice.