Most hotel swimming pools are too short for any sort of serious lap swimming. The pool at the Philadelphia Marriott Downtown is an exception.
This past week I found the indoor 7th floor pool to be adequate and well maintained. Basically a lap pool (2 lanes wide) roughly 25 yards in length (North American winter short course), with a square lounge/play area off to one side. No lane ropes. Bottom lane marks, but none at ends. Ranging 3.5 - 4.5 feet deep. A newish looking vinyl liner. The water was clear, and tasted vaguely of salt (I guess they're using the new-fangled chemicals -- Ph was good). Open 5 a.m. to 11 p.m. I think. Changing rooms with showers adjacent, as well as a larger-than-average workout room with treadmills and so forth. Access with room cardkey.