The Great Mosque in Sana

I only know that most mosques are open only to Muslims, but I don't see how they can tell without mistake who is Muslim and who isn't... perhaps, if you wear their clothes.. anyway, a wander around their exteriors is still worthwile. I recommend you the Great Mosque (on Al-Jamaa al-Kabir), which is the most significant out of around 50 mosques from Sana, for centuries it served as an important Islamic school and centre of learning and contains the largest and most famous collection of manuscripts in Yemen.