Sadly, I am not in that boat. However, I do get to travel to parts of the country that are not as constrained by space as NYC, Salt Lake City being one of them. After asking a travel agent to call around and find the hotel with the largest pool in the area (Marriott Provo!), I am blessed with the best swim training $120/night can buy.
All kidding aside, this is the best pool I have ever had access to since I've started training for triathlons. The hotel even has a smaller, 12 meter indoor pool to draw away the kids. Due to its low level of use, it's best to head to the pool after the sun has set, so you don't see all the dead insects floating around on the surface. I tried to come back the next morning and just couldn't get into the water. Yes, I am a big wimp.
The additional insight I have developed since traveling is that when you're the only one in the pool, you can be a little more flexible with dimensions. This pool is ~16 meters long and 8 meters wide. Therefore, if you swim the "C" path - you can come up with an 18 meter pool with a very awkward push off the wall, further simulating open water swimming (or so I think). Winning!