Kerak Castle sprawls along a narrow ridge above the modern town, a 220-metre-long fortress with vaulted galleries, dark passages, deep cisterns, and a small museum tucked inside. Built by the Crusader lord Pagan the Butler around 1142 as the strongest of the Oultrejordain castles, it changed hands repeatedly: Saladin took it in 1188 after an eight-month siege, the Ayyubids and then the Mamluks strengthened it, and the Ottomans used it as an administrative centre into the 19th century.
Walking the site, you can read the layers in the masonry — rough Crusader limestone gives way to the smoother, darker Mamluk additions. Bring a torch for the underground passages. The view from the southern tip of the ridge drops dramatically into the Wadi Karak, and on clear days you can see all the way west to the Dead Sea rift. Plan a couple of hours. Open daily; entry is included in the Jordan Pass.