The castle is located east of Tartus, Syria, in the Homs Gap, atop a 650-metre-high hill.[3] It sat along the only route from Antioch to Beirut and the Mediterranean Sea. It is one of many fortresses that were part of a defensive network along the border of the old Crusader states. The fortress controlled the road to the Mediterranean, and from this base, the Hospitallers could exert some influence over Lake Homs to the east to control the fishing industry and watch for Muslim armies gathering in Syria.
Sir William, the castle in the movie Kingdom of Heaven that Reynald was trolling the countryside was Kerak, if I'm not mistaken. Krak des Chaevaliers was owned by the Knight's Hospitaller.