For a nice hour in a place of serenity and shade, visit the Jardin Majorelle in Marrakech.  Wander within the paths of this small garden full of palms, bamboo, cacti, coloured pots and buildings, birdsong and pools.  This should take, with a mint tea in the cafe (expensive, but pleasant), an hour or so.

It is possible to take a horse and carriage (caleche) ride to the garden and back, they wait for you. Pay no more than 250 dirhams from the main square.