How can I work out my biceps without any equipment whatsoever?

I want to work on my biceps, but don't want to have to use any equipment. Money isn't the issue. I know dumbbells are cheap. I don't want to have to go to a gym, or a park, or a tree branch. I don't want to have to use milk jugs, water bottles, or any sort of weight. Other than possibly a mat, and a towel or something, I want to be able to do a bicep workout in an empty room. Do any exist?