From bone-filled catacombs to sculpted salt churches to hand-carved cave complexes large enough to house 20,000 people, Underground Worlds is packed with more than 50 unusual destinations that take some digging to find. Award-winning travel writer David Farley revels in the unexpected, whether it is a cave city in China which houses one of the world's largest collections of Buddhist art or an old salt mine converted into a theme park in Romania.

Stunning photos help readers see places they could not even imagine, such as a three-story underground train station in Taiwan that is home to the a 4,500-panel "Dome of Light" that is the largest glasswork on Earth, as well as secret spaces, such as an ornate temple built beneath a suburban home in Italy. Throughout the fascinating text are themed entries of underground systems such as the 2,500-year-old water tunnels of Kish Qanat in Iran or engineering marvels like the New York City steam tunnels.