They arrived in huge numbers on shared bikes after pedaling 30 miles in the evening chill, pumped by the adrenaline of youth and the thrill of embarking on a spontaneous adventure with friends.

The students would emerge on their bikes, in the tens of thousands, seemingly out of nowhere. Like a flash mob on wheels, they rode for hours in the night, by the light of streetlamps, sometimes bursting into verses of the Chinese national anthem.

Nighttime bike rides to Kaifeng, an ancient city in central China's Henan province known for its historic sites and soup dumplings, have been all the rage among college students in the nearby provincial capital Zhengzhou.