The Hassen II mosque is the 3rd largest mosque in the world behind Mecca and Medina. King Hassen the megalomaniac as he know to the political prisoners of Morocco, built the mosque by taxing every family in the country regardless of wealth (or lack thereof) and had the army come to collect from families who were not immediately forthcoming with the cash.
Apart from this ugliness, the mosque is incredibly beautiful and ornate, and one of the only mosques in the world that allows non-muslims to enter. It contains wonderful mosaic tile work, marble, Murano glass chandeliers, acres of carved wood, and a moveable roof that can be opened during large celebrations.
At christmas, it takes more than a thousand workers and 30 billion lights to decorate the mosque. And in the fall, the sunroof is opened and the courtyard is transformed into one the largest Octoberfest celebrations in the muslim world.