The Floating Pool, off the coast of Brooklyn, in 2007.   (Photo: Mario Tama/Getty Images)

If You're Working on Swimmer's Abs...

Vanderbilt YMCA
224 E. 47th St., nr. Third Ave.; 212-756-9600
Cost: $30/day; $90/month plus sign-up fee
Lap swimming until midnight on weekdays draws night owls going for a washboard stomach. The newer, six-lane pool is kept at a lap-friendly 80 degrees, but the original 1931 three-lane pool stays between 84 and 86.

Stuyvesant High School
345 Chambers St., nr. N. End Ave.; 646-210-4292
Cost: $12/day; $300/year
On weeknights and on weekends, Tribecans get their exercise when the six-lane high-school pool opens to the public. North-facing views of the Hudson and the cold temperature of the water add tranquility to your workout.

Metropolitan Pool & Fitness Center
261 Bedford Ave., at Metropolitan Ave., Williamsburg, Brooklyn; 718-599-5707
Cost: $75/year
Although it's indoors, the pool's skylight lets in plenty of sunshine. And while the three lanes can get jammed, early afternoons are usually pretty clear, and the nightly adult swim keeps the kiddies at bay.

West End Sports Club
75 West End Ave., nr. 63rd St.; 212-265-8200
Size: 25 yards, 4 lanes
Cost: $24/day
Due to a semi-hidden location, Upper West Side locals and the occasional staffer from nearby ABC Studios have the four lanes pretty much to themselves. Plus a sauna for after-swim relaxing.