Tunnels

Longest road tunnel in the world features an air treatment plant and the illusion of daylight.

Forgotten German bunkers in China create a sharp cultural contrast.

Special tunnels built so that frogs won't be killed when crossing the highway.

Miles of man-made caves and tunnels are currently used for cultivating mushrooms.

This beautiful natural train tunnel is said to grant the wishes of visiting lovebirds.

A series of gun powder chambers currently hidden from view within Nobbys Headland in Newcastle, Australia.

Deep under Manhattan is the largest construction project in city history. So far, the project has taken the lives of 23 workers, or "a man a mile."

This impressive tunnel was dug entirely by hand over the course of 36 years.

The only remnant of a small mining town is an abandoned railroad tunnel that is steeped in ghostly lore.

A 300-yard long natural tunnel runs through a ridge deep in the Appalachian Mountains.

NYC's legendary underground network for bovine transportation.

A tunnel once abandoned now thrives with graffiti art as an off-limits makeshift gallery.

This eccentrically decorated palace is replete with grottoes, fountains, tunnels, and caves.

This long, dark tunnel is open to hikers, but those without lights are known to get confused even on the straight path.

An underground magnet for ever-changing street art.

The first full-scale tunnel built in America is short but scenic.

An exquisite tunnel of cascading flowers.