This 1400-year-old network of defence tunnels, stretching underground for 10km, are the oldest and longest series of such tunnels in China. Built at the end of the Sui dynasty in case of attack by Tang dynasty invaders, they were never used and subsequently fell into disrepair. Today, 1500m of tunnels on three levels have been restored. You descend as low as 26m in places and tour narrow and low subterranean passages, which were once storage rooms, guardhouses and bedrooms.
Holes cut into the side of shafts leading to the surface indicate escape routes and places where soldiers stood sentry to spy on would-be attackers. Chinese-speaking guides (included in the ticket price) are compulsory; you don’t want to get lost here.
The tour includes a visit to fascinating Zhāngbì Cūn (张壁村), a still-occupied Yuan-dynasty farming village above the tunnels. You can wander its cobblestone streets and temples for free if you don’t mind skipping the underground castle.
You can only get here on tour or by private car (per day ¥350). Check with your accommodation in Píngyáo.