The Grand Mosque, Oman

Jokingly described by some Omanis as a "tourist attraction, not a masjid" or by those less cynical as "a dawah tool for outsiders" the Grand Mosque is undoubtedly the single most impressive structure in Oman and probably the most beautiful masjid I have ever set foot in, outside of Sultan Hasan in Cairo, and Sheikh Zayed mosque in Abu Dhabi (I have yet to travel to Mecca and Medina).