I believe that you can make it onto any pool deck, no matter how exclusive, with a little confidence. Now, I'm basing this off of one afternoon spent with a 100-percent success rate sneaking in (and then swimming in) three Manhattan pools. Maybe I'm not the absolute expert here, but the advice still stands. Dress for the occasion in a one-piece suit (better for all those laps you're about to swim and more versatile for the walk to and from), and layer a lightweight, sheer (if you're into that kind of thing) dress on top. Now that you're on board, schedule stops at:
Gellert Baths and Spa, Budapest : It's likely not near your current location (Oh, hey to the couple ITG readers in Budapest!), but it's still one of the best public pools around. There are indoor pools and outdoor ones, plus everything's heated.
Post Ranch Inn, Big Sur : Coming to our attention via ITG writer Victoria, this place is peppered with small, heated pools that look out onto water, water, and more water. Good for finding your inner peace or whatever.
La Piscine at Hôtel Americano, New York : OK, so maybe you don't want to get a hotel room, and you don't want to sneak in—that's totally reasonable, normal, and understandable. Here you can pay $40 Monday through Friday to get in (free on the weekends on a first-come, first-serve basis as long as you order from the restaurant), sit back, and enjoy from the hotel's somewhat-convenient West 27th Street location.
Amangiri, Utah : Three words: King. Sized. Daybeds. You'll have plenty of room to sprawl out and also have the benefit of being surrounded by desert rocks, which doesn't really offer much particular benefit other than being really cool—practicality isn't exactly top of mind when it comes to luxury daybeds, and that's not a problem once in a while.
LeCrans Hotel & Spa, Switzerland : This appears to be more of a giant hot tub experience, which actually sounds like a great thing. Put a big, heated pool in snowy Switzerland, and that's kind of the effect you'd expect.