Glasgow, Scotland: While traveling for business I happened to stay near the airport at a little hotel called the "Dean Park Hotel". Glasgow was sold out for a conference so this was the only hotel in town with rooms. Definetly not the Ritz! But it has a few great features, excellent bar/parlor area (large) and good food in the restaurant. That's about all I can muster for traditional compliments! However the striking features of the hotel for our purposes are numerous!
One morning I was awakened to that rythmic sound like no other. Then it struck, this place is an ideal hot spot for our underground sport! The beds are as sqeauky as mice and the walls are super thin. The doors have gaps under and are thin themselves. One night I listened to the drunk couple across the hall fuck on the floor because the bed was so noisy.
It sound like I was in the room with them! All from the safety of my room. Also, a quick trip down the halls and you can hear what's happening in almost all. Next, the hotel is in a U shape. So when the windows are open, if you are in a room with a window to the courtyard, you can hear the other rooms (the windows are right above the bed). 
Breckenridge Colorado: The Way Side Inn just outside of town is an old motel/ski lodge. My wife and I have heard couples (mostly young skiiers/boarders) during the weekends even during Summer months. The best listening is in the main lodge on the 2nd floor. There is a false wall that only separates the rooms by the panel ceiling (which are movable). Excellent recording opportunities right over the neighbors room!
The only downside is that the doors are outside. One night we were staying with another couple in the room and could hear the neighbors, however no one seemed to enjoy the sounds but me 
Anyway, you now know of my top 3! Keep me posted if you will be staying at them anytime soon. Good luck, be safe, and enjoy!
