In your visit to Marrakech, you simply can't miss a nighttime visit to Jamaa el-Fnaa. I'd suggest heading around 11pm, more or less, and having a tea in one of the terraces (rooftop, preferably) of the bars that circle the square and soak in the controlled chaos that slowly builds. Snake charmers, stands that pop up out of nowhere, juice vendors, monkeys, women offering to paint you with henna....And, above all, lots of effort to coax the more clueless tourists into the square's restaurants which charge rates way above the normal for Marrakech (in the end, this is an first step in every tourist's initiation to the Arab world! :D). Since a video is worth more than world, I'll leave you a video which I shot.