I spent one day in Casablanca, or Casa as it's known by the locals, which was plenty of time to see the city. The Arabic name for the city is Dar al-Baida, meaning "White House". It's famous mainly from the film 'Casablanca', which was shot entirely in California and not at all in Morocco.
The original medina is really small, since it was only a village when the French arrived. So most of the city is a French 'invention', with lots of art deco buildings in various states of repair and disrepair. The medina itself has a lot of new buildings in it, and there isn't much of the wall left. The interesting buildings are the Art Deco buildings that the French built.
The main 'tourist' site in Casablanca is the Hassan II Mosque, the world's 3rd largest mosque (and largest outside of Saudi Arabia). The mosque is so big that it could fit 25,000 people inside and another 80,000 in the courtyard (quick math = 105,000 people!). The minaret is the world's tallest at 210 metres. Quite incredible to see, and interesting because it's one of the very few mosques in Morocco that non-Muslims are allowed to enter (at a very high ticket price).