THE CHURCH IN THE ROCK
The name may be a mouthful, but Temppeliaukio Church is worth remembering when you're next in Helsinki. Forget big Gothic cathedrals or bland brick houses of worship - this particular place of pilgrimage more resembles an alien spacecraft that's chosen to park for a while in the centre of the city. The flying saucer-like impression is thanks to a vast copper dome which serves as the ceiling, capping a church that was built directly into granite bedrock.
Step inside, and you'll be surrounded by bare, rugged rock - it's not every church that makes you feel like Indiana Jones as you enter. Since opening in 1969, it's become one of the most famous architectural feats of the country, and the brilliant acoustics provided by the natural walls also make it a favourite venue for concerts.
THE OCEANIC METRO STATION
Underground train stations aren't renowned as places to linger and enjoy at your leisure. Even the most handsome examples of London tube stations aren't usually enough to stop people from quickly scurrying their way from platform to exit. But, over in the Italian city of Naples, they've created a number of so-called "art stations" on their metro network, specifically designed to amaze and beguile.
"It isn't a museum in the sense of a repository of art," as the artistic coordinator of the project puts it. "It's an underground aesthetic of the contemporary, bearing witness to our time." However you think about it, it's pretty jaw-dropping. The Toledo station is the biggest looker, with its blue mosaics giving you the impression of descending down the escalator into an ocean world. Adding to the enchantment is the sunlight that comes down through a skylight - a peek of the world left behind by the subterranean travellers.
THE STATUE-FILLED SALT MINE
Wieliczka Salt Mine. It may not sound like a tourist attraction, but this destination not far from central Krakow is one of Poland's most spectacular hideaways. Salt has been extracted from the location since the prehistoric era, with the first mines being dug back in the 13th Century. The end of commercial mining in the 1990s led to its transformation into a gleaming grotto dotted with unlikely artworks, including statues carved from rock salt.
One of the standout sights in this subterranean labyrinth is a detailed salt sculpture of Pope John Paul II, who hailed from Poland and is a beloved icon of the country. Explorers of the mine will also find chapels constructed from the salt, salt-based reproductions of Renaissance artworks, and shadowy nooks which were once used by Nazis to store military materials during World War Two. Even the glittering chandeliers owe their radiance to the mine, with their diamond-like gems actually fashioned from reconstituted salt.
THE UNDERGROUND TOWN
Coober Pedy is way out in the Australian outback, hours and hours away from the nearest major city. Its barren, sun-scorched, other-worldly landscape has made it a popular location for movies - it served as the dystopian backdrop for Mad Max Beyond Thunderdome - though it's best known as the opal capital of the world. Its importance in the gem market means its citizens are willing to brave the harsh, heated conditions.
And they've come up with a clever way of enduring the soaring temperatures. Namely, to live underground. Coober Pedy's soil is home to numerous subterranean houses and hotels, with bedrooms and kitchens boldly built below the Earth's surface. There are also underground museums and an eerily beautiful Serbian Orthodox Church which is entirely enclosed by ornately carved sandstone. As one resident said in an interview, "I even know someone who has an underground swimming pool in her home."
THE HOTEL WITH UNDERWATER ROOMS
Some hotels tower high into the sky, piercing the clouds with architectural aplomb. But the InterContinental Shanghai Wonderland goes in the exact opposite direction, burrowing down through the layers of a once-abandoned quarry. With most of its floors below ground level, it's a sight that defies all expectations, as audacious as the secret lair of a super-villain, and it took more than 5,000 designers, engineers and architects to make this vision a reality. Some of the floors are literally underwater, and come with dreamy aquarium views.
It should be jarring, but the ingenious design somehow makes the hotel look like it's well at home amid the exposed rocks of the quarry. It also makes use of solar and geothermal energy, the surrounding rock helping regulate the temperature within. The structure also sucks up the cool air above the waters of an adjacent pond to provide natural circulation through the ventilation system. Not just a pretty face, then.