Hidden underneath the hilly grasslands studded with ocotillos and mesquite trees in southeastern Arizona lies a world shrouded in perpetual darkness: Kartchner Caverns, a limestone cave system renowned for its untouched cave formations, sculpted over millennia by groundwater dissolving the bedrock and carving out underground rooms, and passages that attract tourists from all over the world.
Vast energy sources are slumbering below big cities. Sustainable energies for heating in winter and cooling in summer may be extracted from heated groundwater aquifers.
In an ambitious project that looks like a cross between a green Millennium Falcon and a villain’s lair from a James Bond movie, France’s EuropaCity is nothing less than a self-contained underground city, only part of it sticks up from the surrounding landscape.
If you've been following EarthTechling for a while, you may remember the LowLine.
NASA's Cassini spacecraft has come up with strng evidence that Saturn's moon Titan is hiding a layer of liquid water under its ice shell.
Geothermal has long been touted as the only stable form of renewable energy because it produces constant 24-hour energy from hot rocks deep underneath the ground.
As much as three percent of Mars could sustain life, say scientists from the Australian National University - but most habitable areas are underground.
Liquid water on the Martian surface was probably never around for very long, meaning life would have struggled to gain a foothold there.
Years ago, I started seeing a lot of record stores that catered to rappers and DJ's by selling albums and turn tables.
An enormous underground river has been reported flowing thousands of feet below the Amazon.
Huawei must be feeling rather hurt. It's offered to foot the £50 million bill for bringing cellphone coverage to the London Underground - and Londoners have given the plan a resounding thumbs-down.
Las Vegas is a city that never sleeps; there is no last call in Vegas. All of the happiness that comes from bright lights, gambling and free flowing booze is a huge contrast to the meager lives of the inhabitants who live below Sin City.
In HG Wells' The Time Machine, the brutish Morlocks live underground, appearing only to service the needs of the beautiful but weedy Eloi.