There's no greater feeling of pre-drink excitement than hitting upon a secret den of cocktails, bonhomie and hedonism.
Heading beneath the surface into the bowels of a building adds a certain frisson to a bar experience.
Not only does a total lack of sunlight give one the excuse to stay until close to breakfast time, many of these subterranean bars have had bizarre former lives as nuclear bunkers and bank vaults.
Now, sensibly, they're devoted to the joys of imbibing.
Converted bank vault (Trinity Place, New York)
Deep underneath a typically Gotham City-esque Big Apple skyscraper in the heart of the financial district, gaining entrance to Trinity Place involves walking through a set of two century-old 35-ton doors, which lead to the former vaults of the United States Realty Bank.
The first room contains a buzzy lounge area and behind the second, a dining room which, according to owner Jason O'Brian, was once the private meeting room for the bank's executive board members.
Food is in a suitably mid-20th century "Mad Men" style -- there's steak tartare and lobster bisque along with high-end craft ales on tap including Smuttynose and Duvel.
Former underground public toilet (Cellar Door, London)
There's still at least one WC in here, right?
It's predictably tiny but the usual vile environs of the London public toilet have been blown apart by this conversion of a Victorian underground convenience into a cabaret and burlesque bar.
Holding just 60 people there's an array of oddities to discover including snuff tobacco available from the bar, opaque toilet doors which only frost over when locked and an SMS jukebox.
London bar and travel blogger Harriet Constable is a regular visitor here and says, "It's got a really loyal following of genuine London eccentrics who come here knowing they can be naughty and not have to deal with oppressive bouncers.
"It's amazing that somewhere this centrally located still has such a cult reputation -- it's been here a while but it's still an 'in the know' kind of spot."
Cellar Door, 0 Aldwych, London WC2E 7DN; +44 20 7240 8848 Cave (Bar More, Dubrovnik, Croatia)
Looking quite startlingly like the underground lair of Dr. Evil from Austin Powers, this natural cave beneath the chichi Hotel More in Croatia's most beautiful city is a fabulous, strangely retro combination.
In the heart of it are precipitous rocky walls illuminated purple, stalagmites and stalactites, glossy white bar counters and some serious mixology from the bartenders.
Ask nicely and they might rustle up the "Crocktail" -- a Croatian specialty made with Zada Maraschino (a local liqueur), cherry juice, lemon juice and candied orange peel.
If the weather's good you can even ascend from the cave and drink it on the terrace above ground.
Bar More, Kardinala Stepinca 33, Dubrovnik; +385 020 494 200 Nuclear bunker (Parukarka, Prague)
If the world ends, best to go down drinking.
You'll struggle to find it when it's dark, but if you're in the Zizkov district of Prague on a weekend evening and you see a tiny doorway in the middle of a graffiti strewn concrete wall with the world "amigo" written on it, you've found one of the strangest clubs on (or under)Earth.
Down two spiral staircases you're in Bunkr Parukarka, a nuclear bunker built by the Czech Communist party in the 1950s.
"It would have been easier to destroy it and then rebuild it from scratch," says Michal Tesinsky, the man behind the three-year clean up job that turned this Cold war oddity into a thriving club, art gallery, bar and live music venue that can hold 250 Prague night owls.
Spookily however, over four fifths of the bunker complex still lies empty.
Stranger still is the fact that one of the stipulations of the use of this incredible space is that, should Armageddon break out, the club must be converted back to its original purpose within 48 hours.
Former brothel (Madame Claude, Berlin)
This subterranean dive was once home to Berlin's notorious ladies of the night, who used this club to "serve" American soldiers in the period after World War II when the German capital was divided into zones controlled separately by the British, Americans, French and Russians.
Converted by three French school friends who all moved to the German capital, the bar is now a warren of rooms with Dali-esque touches of surrealism including an upside down room where tables and lamps hang from the ceiling, a wardrobe leading into a secret bar and a delightfully low admission fee on a "donate what you can afford" basis.
Entertainment veers towards the experimental and avant garde with regular DJ sets, open mic spoken word nights and even ping-pong contests.
Former Crypt (Bedfords, Norwich, UK)
With its stone flagged floor and barrel vaulted ceiling, this bar and live music venue still bears the hallmarks of the 15th-century medieval crypt it once was.
Located in The Lanes, one of the most ancient parts of the historic market city of Norwich, the building upstairs is no spring chicken, constructed in the 17th century and formerly used as a Post Office.
Manager Jamie Jamieson, who has worked at Bedfords for 19 years says: "It's a beautiful space with lots of exposed original features. Every time I show people round they say 'wow.' It has all the old stonework and a vaulted ceiling."
Listed as an ancient monument, the crypt was once used as a creche for the children of the office workers in the main building -- enough to give any child nightmares.
Bombings during WWII meant that many of Norwich's crypts collapsed or were filled with rubble.
This is one of the few survivors, where you can find anything from a DJ night to a salsa dance class -- and even the odd wedding after-party.
Bedfords Bar, 1 Old Post Office Yard, Norwich, Norfolk NR2 1SL; +44 1603 666869