My wife has been an unacknowledged exhibitionist for years--liked the idea but wouldn't act on it except in the most minimal way. Well, recently that changed, drastically.
We were on a road trip and staying at a couple of different hotels. She tends to let the exhibitionist out a little in hotels, enjoying sex by the open curtains and maybe the occasional flash to me in public, but only if she's sure no one is outside or can really see her. She's in her late 40s, a 5' 1", petite, curly auburn hair, with a 34C bust and a nice, round ass.
This time, we were staying at a very nice hotel on the banks of a river across from the downtown district of a major Midwestern city. We were in the top floor of a six-story hotel. To give you a picture of the setup, in order from the window to the back of the room was a large floor-to-ceiling, wall-to-wall window, a king-sized bed, a small sitting area with an armchair, then furthest from the window (about 20 feet) was a nice two-person whirlpool tub. There were the standard wall lights around the bed and a couple of small spotlights over the tub itself.
Across the river from us (only about 500 yards wide) was the downtown section--apartment complexes, restaurants overlooking the river, high-rise office buildings, etc., and directly across from us was one of the largest restaurants on the riverfront, with about 30 tables outside and two large floors of tables inside looking out of damn near 50 yards of plate glass overlooking the river. Behind that was two large 20-floor apartment complexes, and a steep hill behind that covered in houses, apartments, and other living facilities. Overall, there were easily a thousand different windows we could see from our suite.
After we came back from dinner that night, I invited her into the hot tub. Unfortunately and oh what a shame, I neglected to close the curtains

.... By this time, it's dark out, so with just the lights on over the tub, anyone with a set of binoculars could see my wife nude as she took off her clothes and jumped in. I know she noticed the curtains open, but she didn't say anything, so I assumed I could feed her inner exhibitionist. Game on.
We enjoyed the hot water and fondled each other for a while before she took my cock in her mouth. We had been teasing each other all throughout dinner, so while I enjoyed the beautiful effort she was putting into sucking me dry, I didn't want to come just yet, and that seemed like a real possibility. Meanwhile, I had two fingers on her clit, rubbing her pussy and licking her nipples at the same time. She started moaning, so I decided it was time to up the ante.
We got out of the tub, and I tell her I want to fuck her by the window. She agrees, but only if I turned off all the lights. At this point I figured I didn't have anything to lose, so I told her no, I wasn't going to, and that she would just have to deal with people being able to see her. Instead of the expected argument, she simply said okay, and let me lead her over to the window. I faced her towards the river and started rubbing her tits with one hand and her pussy with the other while standing behind her, rubbing my cock up against her ass. She started squirming and moaning again, enjoying the attention and the thought of all those people seeing her. We were backlit by the mood lighting over the tub, so while I'm sure they could see our silhouettes, we were still just shapes in a window.
She's getting more and more turned on. I eventually take her to the bed, face her towards the window on her knees, and enter her from behind. I grabbed her hair and pulled her head up, so she was looking out over the river as I rail her doggy-style. While I'm fucking her, I start talking, telling her how much I love fucking her in front of the window, and how hot it is that so many other people can see her getting fucked. I ask her if she loves getting fucked where people can see her, and she says "yes" in between moans.
I'm getting close, so I stop fucking her for a second, and tell her not to move. I get off the bed, and turn on all the other lights in the bedroom, two of which are between us and the window. Now, we're completely illuminated, a bright room with a picture window overlooking a busy river and waterfront, at about 11:30 on a Friday night, and the best part was when I turned on the lights she didn't argue, just told me to fuck her some more. I get back on the bed and continue to pound her, pulling her head up again so she is forced to look out over the river. I talk more trash, making sure she notices the boat cruising on our side of the river and the people eating at the restaurant while I pound her pussy from behind. Her moans and cries of 'YES!!' after every one of my comments told me just how turned on she was by all those people who could see her.
We fucked for about five minutes that way before I couldn't take any more. With one final thrust, I came deep in her pussy, nearly shoving her off the bed. Spent, I stopped pounding her, but she wasn't done; quick as a flash she almost literally threw me over on my back, climbed aboard, and rode my cock for another couple of minutes while she rubbed her clit. So now she's on top of me, back arched, tits out, head back, showing an amazing profile to the diners across the river as she came, screaming loudly (she's very vocal when she comes hard). Finally spent, she collapsed on me, totally out of breath. we lay that way for about five minutes, her ass in the air, still with the lights on and in full view of the city.
That was the FIRST time she surprised me with window sex that trip.