This just happened to me this weekend. It was completely unexpected and one of the hotter things I've ever experienced. Two weeks ago I (24m) had posted on my local subreddit (/r/brisbane), asking what kind of sober events are on during the weekend. I got a few replies, one in particularly from a 22 year old (who we'll call Sarah) saying that she'd be interested in doing something as she was new to town. I didn't end up doing anything that night but we began casually messaging.
Two week after this we've sent a few messages per day to each other and I'm not thinking anything of it. Then the conversation turned a little dirty and we discussed the idea of fucking a total stranger. We both got turned on by the idea as by this stage neither of us had even seen what the other looked like. We decided that we would do it, and Sarah sent me her address.
On the drive over I was nervous, I really didn't know what I was getting myself into. Sarah had told me how to get to her door and had mentioned that she'd leave it unlocked. I rolling the dice big time, I had no idea what this girl looked like and here I was, committed to fuck her.