Cave

Storing clean energy to use later poses a challenge in regions that have long stretches with low wind and sunlight, stressing power grids fed by renewable sources. Augwind Energy believes it's found a solution thousands of feet below the ground.

To prepare for space exploration, the ESA has been testing techniques and training astronauts in cave systems on Earth. The group's latest tool is a crash-proof drone that could one day help Martian settlers explore lava tubes on the Red Planet by mapping out tight spots humans can't reach.

"It's an interesting thing with passive solar design," muses Lionel Buckett, "that a cave facing north is probably the first passive solar building that humans ever lived in." And that's what this master builder has created, on a spectacular 600-acre property in Australia's Blue Mountains.

A Vietnamese resort company has been granted approval to begin surveys to build a 10.6 kilometer long cable car in the world’s largest cave, the UNESCO-listed Son Doong in north-central Quang Binh province in Vietnam.

The old Blaenau Ffestiniog slate mine in North Wales is soon to become the home of the world's largest underground trampoline. Set to open on Friday, Bounce Below is the newest attraction to the Zip World theme park.

Switzerland's Peter Kunz Architektur is responsible for the creation of a modern day “Batcave”-style garage.

Deep within the dark tunnels and cavity shafts of an old Swedish silver mine, guests can sleep in the world's deepest hotel suite.

An underground atomic shelter has been transformed into an internet provider's HQ.

A home entertainment enthusiast 'Down Under' in Melbourne, Australia, has built a unique home theater - his very own Bat Cave replica.