IT'S THREE A.M. WANT SOME ONION SOUP AND OYSTERS? FEEL LIKE SHOOTING SOME POOL? HOW ABOUT GETTING A HAIRCUT? NO PROBLEM. THE CITY OF LIGHT HUMS AT ALL HOURS. . PHOTOGRAPHS BY SEAN McCORMICK.

YOU'RE IN PARIS AND YOU CAN'T SLEEP. MAYBE YOU'RE EXCITED TO BE HERE, MAYBE YOU'RE A HOPELESS NIGHT OWL, OR MAYBE YOUR BODY CLOCK SIMPLY HASN'T CAUGHT UP WITH PARIS TIME YET. YOU MIGHT THINK THAT THE ONLY BUSINESSES OPEN 24 HOURS A DAY IN THIS CITY ARE A FEW STRAY GAS STATIONS OR BARS. YOU WOULD BE WRONG.

Look around and you'll find a surprising number of places advertising "24h/24" or "ouvert jour et nuit" (open day and night), and they come in a variety of flavors.

Here's a miniguide to a few of the places that are (almost) always open and waiting for you when you can't - or won't - sleep.

EAT, EAT, AND EAT SOME MORE 
Hungry? With such a foodcentric culture, Paris naturally has a fair number of eateries that simply never close their doors. Others remain open through the night, shut down for an hour of prebreakfast housecleaning, and then get right back to business. You needn't go hungry at any hour.

One 24-hour restaurant that is bursting with tradition is La Tour de Montlhéry, also known as Chez Denise, which looks as if it's ready for a film crew to start shooting a bistro scene in a French movie. Chez Denise once served denizens of Les Halles, the wholesale-market area known as "the stomach of Paris." While the market has been gone for nearly 40 years, the bistro has never surrendered - nor even changed its menu much. You can have fish and vegetables if you insist, but customers usually come for platters of charcuterie; giant servings of steak frîtes, pot-au-feu, calf 's liver, and whatever other meat dishes are on the blackboard; and a side of the house homemade fries.

An old market haunt that's also still around is Au Pied de Cochon, a jolly brasserie that impresses diners with its signature onion soup, all manner of shellfish, and specialties made of parts of the pig that even the pig didn't know it had. The late crowd - a mix of theater types, club-goers, and tourists - orders from a night menu that's priced a bit higher than the regular list.

The owners of Au Pied de Cochon, the Blanc brothers, have a total of 15 brasseries in town, two more of which are centrally located 24-hour spots: Le Grand Café des Capucines, near the Opéra Garnier, and L'Alsace, on the Champs-Élysées. Both offer a broad menu that leads off with half a dozen kinds of oysters and a roster of other shellfish. All three of these Blanc brothers establishments double as all-night specialty-seafood markets, selling Normandy and Brittany oysters to go at any hour. Crates of the crustaceans are part of the house decor.

Around the corner from L'Alsace are La Maison de l'Aubrac, a beef house with an unexpectedly ambitious wine cellar, and Café le P'Elysées, a great place to head to for a light meal and a beer.