The Jama Masjid Mosque consists of a central courtyard surrounded by arched walls, and the mosque itself. The entrance is free, but you have to pay for a camera ticket.
To enter the mosque you have to cover your legs and arms, and leave your shoes at the entrance. For a fee you can climb its minaret, from where there is a nice view of Old Delhi.
In one of the corners of the courtyard there is a stone with the footprint of Muhammad.