Sheikh Zayed Mosque, Abu Dhabi

The Mosque took 11 years to build and was the project of Sheikh Zayed bin Sultan Al Nahyan. It is one of the largest in the world. 
The mosque is large enough to accommodate over 40,000 worshippers, while the main prayer hall can hold over 7,000. It features 82 domes, over a 1,000 columns, 24 carat gold gilded chandeliers and the world's largest hand knotted carpet.
A must-see if you are going to Abu Dhabi.