MEDA'IN SALEH, Saudi Arabia (Reuters) - Sheltered from the world by an ancient religious curse and modern Middle East conflict, a spectacular ruined city lies almost hidden in the northern deserts of Saudi Arabia. More than 100 tombs and burial chambers are carved elaborately into rocky outcrops across the sands of this city, still bearing names and ornate religious symbols chipped into the sandstone 2,000 years ago. Nearby volcanic mountains, decorated with the 10,000-year-old art of prehistoric hunters, tower over a palm-filled oasis and an abandoned mud house village. Through them all snake the remains of an Ottoman railway, built...