Practising without a piano

I once saw in a drama a girl who had to practice piano on a keyboard drawn out on a piece of cloth and now I read about a man in prison who taught himself piano from books and practising on a cardboard keyboard. It is amazing to read about such determination. I do not think I can do this. Absolutely full of respect for this man.

http://www.newyorker.com/culture/culture-desk/my-cell-learning-to-hear-on-a-cardboard-piano