Not sure if this is "porn scene" enough, but I'd say the closest I've been to it was a drunken night in Gran Canaria.
To give you bit of background I was there on holiday with my then boyfriend. We'd gone out drinking one night and gone into a leather bar with a darkroom and play area. Darkrooms aren't really my thing (at the time I'd never been in one), so I was happy having a drink in the bar area, but my bf wanted to check out what was thru the back. I was a bit reluctant at first, but it was early in the night and the bar wasn't that busy, and between my bf and my own curiosity I agreed to have a look thru. Going in, the first part was really dark, apart from the odd UV light, then further back there was some very low lighting, I remember passing by an empty bath tub, which I presumed got used for piss play. I remember there was a couple fucking in a sling, that we watched for a little, before finding that there were some cubicles, watching the guys in the sling had made us both horny, so we went into one and had sex, I have to admit it was pretty hot doing it in there.
Anyways, once we were done we headed back out to the bar, well I say we, I did, the bf didn't make it all the way back out. I went to the bar not realising and thinking maybe he'd popped to the loo, so I waited a little and then realised he was still in there. So I went back in to find out what he was upto, only to find him sucking some stranger off in the darkroom, his white shirt shining under the UV light - which I guess he didn't realise. I turned around and walked out of place, mad as hell and got a taxi back to the complex we were staying at.
So the porn scene bit:
As I walked past the pool to get to our bungalow, there were four guys in the shallow end of the pool, naked getting down to business, instead of keep on walking I stopped and perched on the end of one of the sun loungers and started to watch the show, they were all pretty into each other and hadn't noticed me walking past or watching, I can't remember how long I was sat watching before one of the guys noticed me, he smiled and started to come over to me, I stood up but instead of turning and leaving I just kinda froze, he got to me and started to kiss me, I kissed him back and he started to undress me, we kissed some more and he led me into the pool, and back to the group. It became a blur of kissing, fondling, wanking and sucking and the feel of the other guys against me and the water was so horny.
It all feels very surreal to think back on, complete chance and something there was no way I would have done normally.