The stars seem to frequent the Gansevoort, which means so do the paparazzi. Consider leaving this one as a last resort.
Marriott Marquis Hotel
Apparently the rooftop bar is dark and skyline views are perfect for setting the mood.
Carlyle Hotel "A bastion of romance" for a more sophisticated/mature/old unfaithful bastard.
The undercover espionage vibe is in full effect here. The lighting is dark not dim, the color scheme is smoke in every shade of grey. The only drawback the is two- floor lobby you have to sneak past before getting to the elevators. At least nobody will be able to make you out.
The pool the 23rd floor could be used for skinny-dipping, oops, getting wet, oops, um... swimming. Just get a room.
First of all, this hotel is located in Long Island. No one is going to find you all the way there.
If you're really going to do it, if you're really going to break your vows, destroy your life and sink to the lowest of low, you might as well go out in style. Besides, the divorce is gonna cost you so much you won't even notice the hight "affair" hotel bill.