Beneath us lies a world of romance, intrigue and tragedy. Not just amazing caves, grottoes and lakes, but also ancient cities, ultra-modern hotels and secret passages under medieval palaces.

Waitomo Glowworm Caves, New Zealand

This network of caves and grottoes is famous for its acoustics. Kiwi opera diva Dame Kiri Te Kanawa has performed in The Cathedral cave and the famous glowworm grotto, where the tiny insects create the effect of a starlit sky.

 

Carlsbad Caverns, New Mexico

The Carlsbad Caverns are the result of reef formations millions of years old, and are full of giant stalactites, stalagmites, cave pearls and helictites. But be warned – at night, thousands of bats leave the cave in a swirl of black wings.

 

The Maginot Line

A network of tunnels, bunkers and fortifications on France’s border with Germany and Italy, it was ultimately a huge military blunder as it failed to prevent a German invasion in World War Two. The Maginot Line is preserved in places, and is recognised as an impressive if futile undertaking.

 

The Underground Cities of Cappadocia, Turkey

In the seventh century, Christians escaping from Roman invasions built underground cities. Since the 1960s, 30 of these cities have been rediscovered. Explore Derinkuyu’s and Kaymakli’s stunning architecture, chapels, cellars and stables.

 

Jules’ Undersea Lodge

Sleeping with the fishes is survivable at Jules’ Undersea Lodge off Key Largo, Florida. To enter the hotel, visitors need to dive seven metres beneath the ocean’s surface. The water lodge is the first of a number of underwater hotels being developed in the US.