I haven't had much of a chance to do this lately because the area where I work isn't a huge touristy area. It's a business and yuppy district. It's not that exciting. But it is nice here, so they do come out in the summer to walk around and especially because it's been so warm out lately.
I used to do this when I was still in school. We had tourists on campus all the time, doing the Universal "I'm Lost" Gesture of scalp scratching and squinting at maps, occasionally accompanied by loud, angry yelling at the male travel companion for one reason or another. Usually because he came Second in the Idiot Contest, he was too much of an idiot to come in First.
I just go "Hi, you kinda look lost, did you need some help?" and take it from there. I think because I'm small, Asian, female, well-dressed, well-kempt, etc. people trust me.
Sometimes, they're not lost, they're just engaged in the classic linear optimization problem of how best to go about doing all these things they want to do while they're here.
So, that was a small bit of non-work.