This garden and now museum was once home to fashion design Yves Saint-Laurent. The garden itself has a lot of lush plants, a stark contrast to the desolate and dirty medina, and makes for a nice peaceful break from all the craziness of the city. If you go it's worth going into the museum for a look at the collection traditional north african textiles, jewelry, and ceramics. I recommend going to Jardin Marjorelle right when it opens the garden can get quite crowded which subtracts from its beauty.
La Maison Arabe Hammam
Just about every hotel in Morocco will have a hammam. This is a special spa where a lovely lady will scrub your skin with a rough luffa until all of your dead skin is off. It's a bit uncomfortable but your skin will feel like a baby's bottom when you are done. After your scrub get a massage and I bet you'll be served mint tea. I went to the hammam in the basement of La Maison Arabe and had a wonderful experience, the setting was also very beautiful and relaxing.
There are several beautiful mosques in Morocco and Koutoubia Mosque is not exception. It's located across the street from La Mammounia and worth a walk through the garden and a viewing of the gorgeous pink brick.