Sure, the lights are dimmed to create a bluish glow, and as you walk down clear steps to get to the dance floor, you can spot the back of the DJ booth.

But the boys still line up on one side of the room, and the girls are on the other, all awaiting instruction.

Only here, at Lima, a swanky K Street lounge, the boys and girls are adults, and they are significantly better dressed than adolescents. Plus, there's an open bar for women from 9 to 11 p.m., an antidote for jumpy nerves to accompany the Monday night salsa lessons that bring everyone here.

Enter the downstairs lounge and you'll find yourself swimming in a soup of attractive, single, well-coiffed 20-to-30-somethings. What's more -- is it possible? -- the ratio of men to women is actually tipped in the women's favor, about 55 percent male.

Follow their eyes, all rapt with attention, and they'll lead you to instructor Earl Rush, a boisterous, middle-aged man from Northeast Washington who has made it his mission to make sure someone in this city can do more than two-step.

Rush's classes, which start at the beginner level and get progressively more advanced, consist of a free five-week rotation. (Yes, that's right, free). Rush takes his students from basic steps to complicated turns, combinations and transitions.

And he's always counting: "5, 6, 7, 8!"

Rush is not an advocate of just "feeling" the music. "What if the woman you're dancing with isn't feeling the same thing you're feeling?" he said.

Rush breaks down the steps first, slowly, and builds until he has a sequence that will last a couple of bars before turning up the music. Then it's time to switch partners and move on to another set of steps.

But even when you're constantly switching partners, it's still possible to get nervous.

"I'm always self-conscious," said Nadine Szablya, a Johns Hopkins University graduate student. "After just a minute, you're trying to concentrate on what they're telling you to do. Then it kind of goes away a little bit. And having a drink definitely helps."

It's not as though salsa lessons are uncommon in the city. They've become as ubiquitous in the D.C. night-life scene as cupcakes in a dessert conversation.

"Everybody goes to the same class and learns the same steps, and that's why no one in Washington, D.C., can dance," Rush said. "I'm here to change that."

But there are some differences. For starters, all the lessons at Lima, not just the first one, are free. Two, Rush's classroom -- the dance floor -- is pretty big and pretty crowded. If you're really earnest, or a slow learner, show up early to stake out a good spot, because the later it gets, the less room there is to move. Still, it's a good, inexpensive place to make new friends or score a date.

Sean Luck, a physics graduate student at Catholic University, started going to lessons three weeks after moving to the city. His prior formal dance training consisted of learning a waltz for a high school production of "Cinderella." But he figured it was a good way to meet people in a new city.

"He's a good teacher," Luck said of Rush. "He breaks things down simply, and he does a lot of demonstrations. He makes it fun and interesting."

Lima 1401 K St. NW 202-789-2800, no cover. Beginner classes: 9-9:45 p.m.; intermediate classes: 9:45-10:30 p.m. Women should wear shoes meant for dancing: something with a moderate heel, but still comfortable, that allows you to twist and turn on the balls of your feet. A-line dresses and skirts that flair out are popular because of the swish they make when a partner spins you. There's no commitment at Lima. You can show at any point during the five-week cycle of lessons, but there are people who come every week. The next beginner class is Monday. Interested in salsa but Monday doesn't work for you? Rush teaches other classes, at $10 per lesson, at these locations in the city, all from 9 to 11 p.m.: Station 9, 1438 U St. NW. 202-667-1661. Third Thursday of each month: Bambule, 5225 Wisconsin Ave. NW, No. 2. 202-966-0300. Sunday: Lucky Strike, 701 Seventh St. NW, No. 2. 202-347-1021. And a note about tipping: There is an etiquette to tipping on open-bar nights. Even when the alcohol is free, the bartender still needs to be paid. Paul Harris, a bartender at Lima, said he thinks $1 per drink is reasonable.