Dominating the city is the beautiful minaret of the famous Koutoubia Mosque, which dates from 1147 (although it had to be knocked down and fully rebuilt in 1199 because a mistake had been made and it was not correctly aligned with Mecca), and can hold some 25,000 people at worship, non-Moslems are not permitted to enter the mosque except under special circumstances, and this tradition should be fully respected.
Also of interest, the Medina (old city) is where you will find the many souks and bazaars that mark Marrakech as a city of traders, and from where you can buy pretty much anything, from essential oils through to televisions at knock down prices.
For a real insight into the history of the city, and the local Berber people, then head to the Dar Si Said Museum, where there is a large collection of their art to browse through, and even the building that houses the museum - a former palace is a treasure in itself.