This is a rare opportunity for non-Muslim travellers. You can enter the mosque of Tin Mal, walk around all over it and have a good look at the details.
You may even enter the roof, which has doubled as a minaret. From here you can look down into the prayer hall of the mosque. That is, if you come to visit Tin Mal within in the next couple of years. There are plans to build a roof over it all, as the last part of the restoration.
Most of the interior is lost. It is actually just the mihrab (the niche that indicates the direction of Mecca for the prayers) and the colonnade in front of it that is well-kept. The rest of the columns are new, and made simple in order not to be confused with the original structures.