Mandu is a sightseeing town in the purest sense: almost everything worthwhile is a palace, mosque, tomb, gate, tank, or viewpoint left by the Malwa sultans and later rulers. The sites are scattered across the plateau, so group them by area rather than trying to walk from one end to the other.
The Royal Enclave and Village Group are the essentials. The Rewa Kund group is quieter but gives Mandu its most atmospheric views, especially late in the day.