Gyaur Kala

Gyaur Kala, the oldest and best-preserved oasis city on the Silk Road and a UNESCO World Heritage Site, is home to the intriguing remnants of the ancient Gate to Central Asia. The archeological site has a 20-hectare walled enclosure that spans 4,000 years of human history (49 ac). The ancient metropolis, which claims to have been the world's largest city in the 12th century, has layers of civilizations, including Persian, Hellenic, Arab, Seljuk, Mongol, and Khiva, with the Zoroastrian "gawurgala," or infidel's fortress, being the most intriguing stone structure.

The location, which is 30 kilometers (19 miles) west of Mary and near the Murghab River, also includes a well-preserved Seljuk sultan's mausoleum. Hire a local guide to help you make sense of the gigantic eroding pillars and abandoned stone structures, and you'll gain a better feel of the history.

Location: Merv, Turkmenistan