Granted I'm not American and 99% of my friends aren't either, but I'm still amazed that not one of my friends who have visited Morocco has visited the American Legation in Tangier.
A working legation from 1821 until 1956, it is now a museum and serves to illustrate through art, furniture, maps (by Mercator), carpets, letters, and objects d'art the history of the relationship between the United States and Morocco (Morocco being one of the first countries to recognize the US as an independent country), as well as Tangerine history. For WWII buffs, the Allied Forces planned part of their 1942 North African landings in these rooms.
Of special interest to me was its museum-within-a-museum--the Paul Bowles Museum. As an ardent Bowles' admirer, I visited the Legation primarily to experience the spirit of the man who wrote, among other works, The Sheltering Sky and to touch his steamer trunks and sit in his chair.
Admission is free. Guided tours are available.