The sign in the window says "retro arcade and museum." Retro, because most of the arcade games inside this Lake Street storefront were considered cool -- 25 years ago. A museum, because in the age of Wii and PlayStation 3, these stand-up game cabinets are relics from another time.

This is Rusty Quarters, the only vintage arcade in the Twin Cities. The small business, containing 21 old-school arcade games, is owned by proud geeks Sage and Annie Spirtos.

On a recent night, Sage was holding court behind his iMac inside the arcade. He wore a "Donkey Kong" T-shirt with the phrase "Going Bananas" splayed across his belly. A group of young boys was jostling for position in front of a three-player game.

"Our biggest money-maker is 'Rampage,'" he said of the 1986 game. "It's a no-brainer. You just go around smashing stuff."

If only life were that simple.

Sage and Annie opened a comic book shop in this same location in 2010. It didn't do well, so they tweaked the concept, turning it into a novelty toy shop. While the colorful merchandise wasn't selling, the lone "Donkey Kong" arcade game in the corner was a hit. People just kept pumping quarters into this 30-year-old machine. It got to the point where players would be standing outside waiting for the store to open.

So Sage and Annie began scouring Craigslist and calling arcade dealers nationwide. In time, the couple amassed a respectable collection of vintage cabinet games. They opened Rusty Quarters on Dec. 28; it's been packed ever since.

It's easy to see why. Each game costs one quarter. Huddled in front of the machines are thirty-somethings reliving their youth, hipsters on their way to Bryant-Lake Bowl and parents showing their children what nostalgia looks like. On quarters alone, this business is surviving. "We're doing pretty good," Sage said. "Not enough to be millionaires but enough to keep the lights on."

One game, "Asteroids," is from 1979. The other classics are all here: "Frogger," "Joust," "Ms. Pac-Man." Sage said he's interested in a few titles from the 1990s, but most of that decade's games were lost to the junkyard.

Retro arcades like Rusty Quarters are rare, mainly because the games are hard to come by. Chicago has a similar arcade. New York is home to a couple (one with a bar). "These machines have essentially been hunted to the point of extinction," said David Hansen, a regular.

Sage said Hansen, 30, is one of the best players he's seen at Rusty Quarters. The freelance writer holds the arcade's high score on "Donkey Kong" (557,000!).

Great "Donkey Kong" players are special in and of themselves. There's even an acclaimed full-length documentary -- 2007's "The King of Kong: A Fistful of Quarters" -- which documents a rivalry between two of the world's best. While its graphics are rudimentary by today's standards, the gameplay is immensely difficult.

For Hansen, there is something poetic about mastering these machines, especially "Donkey Kong." "I find the graphics to be really beautiful and engaging," he said. "They conceal the true nature of the game. It's tremendously cerebral. People who have played it for 25 years still discover new elements they never saw before. I often wonder, 'Did its makers know they were building a game that was bottomless?'"

Sage tries his best to keep these collectors' items in pristine condition, but that means performing daily maintenance. Coin slots get jammed. "Frogger" has a bad capacitor.

"'Q*bert' has blown a fuse," he said. "I have to go to Radio Shack."

Day after day, Sage and his wife are making a business out of this museum of old sensations, one quarter at a time.