I'd have to say it was in the desert, the camel ride out at sunset was awe inspiring and great fun, although a little sore. I do recommend some Sudocrem in your luggage! I'd recommend getting up early to watch the sunrise as you'll catch the night sky and the stars are breathtakingly clear. A little piece of my heart will always be sat on that sand dune watching the stars and the sunrise appearing in the East.
Also the Atlas mountain trek was beautiful and such a deep contrast from the red rocky landscape that is your usual companion. We arrived to thunder and downpours which left the roads very muddy but it was exciting and dramatic, rainbows galor. Although good hiking shoes are highly recommended. The visit to El Glaoui's ruined palace in Telouet was also quite beautiful.
Apart from the Sudocrem and the good hiking shoes I'd say dont be put off by the daunting thought of Marrakesh, it is a little shocking and I dont advise going off on your own but it truely is something you have to experience at least once! The locals are extremely friendly, so dont be afraid to barter for that exotic item, its also great fun to do so. Although a Muslim country you dont feel intimidated at all by this, the locals are very open and as a woman I felt quite comfortable. Even one old man in the Souks of Marrakesh came up to me after Id just bought a beautiful silk scarf and said how beautiful it was and how it matched my eyes. He didnt want anything, just wanted to share his thoughts with me, it was such a nice memory.
What else, pack light but do bring some spare trousers as it can get muddy and like me you could fall over and rip your trousers! A small sewing kit is advisable. Dont worry too much about a season 3/4 sleeping bag, I went in November and the desert was quite warm, a season 2 would suvice but dont go any thinner as the mountain Gite is rather chilly! Might be worth leaving the mobile at home too as although I had a signal, getting through was impossible, a really bad network.
Other medicines are advisable, especially Diarrhea tablets. Always wipe cutlery and glasses that may have been washed under tap water. Avoid salad or unpeeled fruit altogether, its just safer.
Also bring a notebook and pen, its nice to jot down your memories if you like writing. :)
Also maybe pay that little extra and get the single supplement, get your own room if travelling alone because you never quite know who you may end up with.