How do you open a safe without having the keys ?

Some old safes had a thin plate on the bottom, followed by 3 or 4 inches of concrete, and another thin plate. If you can turn it over and unbolt the plate there's a chance you can bust the concrete out with a large hammer.

I've seen it done to a safe where I once worked, supposedly there was nothing in it but papers and nothing taken. We were always a bit skeptical. Whoever did it took the time to fix themselves a glass of water and left it sitting on the boss man's desk.