Jordan is a sovereign Arab state in the Middle East. The capital, Amman, is Jordan's most populous city as well as the country's economic, political and cultural centre. Major tourist attractions in Jordan include UNESCO World Heritage Sites such as Petra and Umm ar-Rasas, ancient cities such as Amman, Aqaba, Madaba and Jerash, the Jordan River, the Dead Sea, Mount Nebo, and locations such as Wadi Rum and the Jordanian Highlands. Other opportunities include shopping, pop-culture tourism, medical tourism, educational and cultural tourism, hiking, snorkeling and scuba diving among the coral reefs in the Gulf of Aqaba. In 2017, Jordan recorded more than 3.8 million tourists. Main tourist destinations Ancient sites Petra in Wadi Musa, home of the Nabataeans, is a complete city carved in a mountain. The huge rocks are colorful, mostly pink, and the entrance to the ancient city is through a 1.25 km narrow gorge in the mountain—called the Siq. In the city are various structures, all (except 2) are carved into rock, including Al-Khazneh – known as the Treasury – which has been designated as one of the "New 7 Wonders of the World" by the for-profit New Open World Corporation. Other major sites of interest in Petra include the Monastery, the Roman theater, the Royal Tombs, the High Place of Sacrifice. The ruins of Petra were rediscovered by Swiss explorer Johann Ludwig Burckhardt in 1812. It was inscribed as a UNESCO World Heritage Site in 1985. Umm Qais, a town on the site of the ruined Hellenistic–Roman city Jerash is famous for its ancient Roman architecture, with colonnaded streets, Corinthian arches, outdoor Roman theaters and the Oval Plaza. Shoubak with its Crusader castle, "Crac de Montreal", marking both the eastern and southern frontier of Crusader expansion. Ajloun has a medieval Crusader castle Al-Karak contains an important castle from the times of Salah al-Din, known as Al-Karak Castle. Umm el-Jimal, the so-called "Black Gem of the Desert", was once a town on the margins of the Decapolis. Rural and well to do, it was a fitting contrast to the surrounding busy cities. Its black basalt mansions and towers, some still standing three stories high, have long inspired poets. Qusayr 'Amra, one of the best preserved Umayyad Islamic period monuments. Its interior walls and ceilings are covered with unique frescoes, and two of the rooms are paved with colourful mosaics. It, too, is a World Heritage Site.