The Japanese restaurant Kenka, located on a bustling East Village block, is easy to miss. Neither its name nor its street number appears on the shop’s exterior sign (not in English, anyway), and there are often so many people milling about out front that you can walk right by without realizing you’ve just passed a restaurant.

There are two good ways to spot Kenka, however: The first is a huge statue (sometimes misidentified as a beaver or a raccoon, although it’s actually a badger) that stands sentry just outside the door. The other is that people emerge out onto the sidewalk carrying small sticks of cotton candy.

That’s because Kenka (25 St. Mark’s Pl., 212-254-6363) has a cotton candy machine near its exit. When the waitress brings the check to the table, she also brings some small cups of pink sugar — one for each member of the party. Diners can then stop at the cotton candy machine on the way out, pour the sugar into the machine, and then use a chopstick (instead of the usual paper cone) to gather the sweet strands into a single-serving treat to go. It may not be very Japanese, but it’s a charming way to end a meal, and it’s why people almost always leave Kenka with smiles on their faces.

Kenka is one of several Manhattan eateries serving cotton candy these days, usually gratis. It’s pretty much a win-win for everyone involved: For the restaurants, cotton candy is extremely easy to make and costs almost nothing (a serving is literally just a spoonful or two of flavored sugar); and for customers, cotton candy is a nostalgic reminder of childhood and a taste of the county fair in the middle of the big city.

Cotton candy is a product of heat and centrifugal force. The flavored sugar is poured into a spinning, heated cylinder in the center of the machine. As the sugar melts, it’s spun out through tiny holes in the cylinder. The molten sugar then solidifies into strands and accumulates along the machine’s inner walls, where it can be gathered up.

The concept of spun sugar, produced by cumbersome, makeshift means, goes back at least to the 1700s. But the origins of mass-produced cotton candy as we know it today — or “fairy floss,” as it was known in its early days — are harder to pin down. Some sources claim that the confection was first popularized by the Ringling Brothers circus in 1900; others point to the 1904 World’s Fair in St. Louis (which, according to lore, is also where hot dogs, ice cream cones, peanut butter, and iced tea made their debuts, although all these claims are disputed).

The one indisputable point is that a pair of Tennesseans named William Morrison and John Wharton were granted a patent in 1899 for a device “in which a revolvable or rotating pan or vessel containing candy or melted sugar causes the said candy or melted sugar to form into masses of thread-like or silk-like filaments by the centrifugal force due to the rotation of the vessel.” Their schematic drawings show a machine very similar to the ones still used today. A century later, cotton candy shows up in some unexpected places. At BLT Fish (21 W. 17th St., 212-691-8888) — the seafood entry in Laurent Tourondel’s growing BLT chain — diners on the restaurant’s more formal third floor receive a glass jar of green apple cotton candy at the end of their meal. It’s a beautifully simple presentation: The confection almost seems to float in the jar, like an ethereally cumulus cloud. “It just seemed like a fun thing to do,” the restaurant’s pastry chef, Shawn Glenn, who previously made cotton candy at JUdson Grill, said recently. “But we go through a lot of it, so I have to make a big batch of it as soon as I get in each day, and several more batches as the night goes on.” The resulting treat tastes a lot like an apple Jolly Rancher.

There is also a cotton candy machine in the kitchen at Landmarc (179 W. Broadway, 212-343-3883), for tables that include children — or at least that’s the idea. “I get at least six or seven requests for it every night from adults,” bartender Jason Ackerman said one recent evening. “Once one person has it, then another person sees it and wants it, and then it snowballs from there.” No upscale glass jar treatment here — the candy is mounted on a traditional paper cone — but the flavors rotate each day (it was grape on the day I spoke with Mr. Ackerman), so there’s still a nice element of surprise, even for regulars.

The most spectacular cotton candy rendition, perhaps unsurprisingly, is at the Four Seasons (99 E. 52nd St., 212-754-9494), where a huge mound of white spun sugar is served atop a generous serving of ice cream, with a candle stuck in for good measure. It’s sort of like baked Alaska, but with cotton candy substituting for the cake.

This dessert isn’t on the menu but is available, for $10, upon request (the Four Seasons prefers that you order it in advance — ideally when making your reservation). Despite this low profile, it’s become one of the restaurant’s signature items. “It’s popular with all ages and genders and sizes,” the restaurant’s reservationist, Julius Mariano, said, sounding a bit like a circus ringmaster.

“After all,” he added,”it’s cotton candy.” His unspoken “What’s not to like?” hung in the air for moment, and then vanished, like a whisp of spun sugar.