Shoubak Castle, also known as Montreal, is a Crusader fortress on a lonely hill north of Petra. Its ruined walls, towers, churches, and passages are rougher than Karak's, but the setting is superb: dry highlands, long views, and a strong sense of why this road mattered.
It makes an excellent stop on the King's Highway or a half-day trip from Wadi Musa if you have your own transport. The ruins require some imagination and sensible shoes, but the reward is a much quieter medieval site than Jordan's better-known castles, with the landscape doing half the storytelling.