The relics of military beacon towers, kilns, graves, city walls and a reservoir－though now mere faint remains in earth tones－echo like voices from the dust about life and ordinary people at the frontier fortress, Wu said.

A tourist commented on Ctrip, an online travel agency, that leaving Yangguan Pass is like going abroad long ago. Tourists can buy an ancient version of a passport, write their names on it and get it stamped before being checked at the gate. Without the document, tourists have to answer a question about the Silk Road to pass.

"It was very interesting!" the tourist said.

She said tourists can reach the relics by camel, horse, mule car or electric car.

"Words cannot express my feelings when I saw the ancient Yangguan Pass. Who could imagine that below the sand a whole city is buried?" she said.

Travel agencies provide two typical tourist tracks in Dunhuang:One day to visit the Mogao Grottoes, Echoing-Sand Mountain and Crescent Moon Spring－the most famous scenic spots near the downtown area; or a one-day drive to the western line－Dunhuang studio city, West Thousand Buddha Caves, Yangguan Pass, Yumen Pass and Yadan National Geological Park.

Direct flights are available from Chinese cities including Beijing,Shanghai and Lanzhou, capital of Gansu. Deep discounts for tickets and hotels are offered from December to the end of March to promote winter tourism.

Information registration, body temperature checks, reservations and masks are required for epidemic control.