In the old east part of town, this is a large old, somewhat derelict and entertaining art workshop. It has a lively bar, with huge garden and installations.
It is on Oraniensburgerstrasse, opposite the bar Obst und Gemuse (literally fruit and veg!)
Updates
If you want to only meet tourists, Tacheles is the place to be. Its best days were in the early 1990s, today it's generally full of Brits and Australians on "pub crawl" tours.
Is this your business?