How do you recommend making friends in a foreign city?

So I’m having a great time in Paris and I’ll be here for two months. I’ve met a few of the kids in my student hostel but they are definitely kids. I am by far the oldest; they are between 17–20, and we don’t have much in common, nor do they have much interest in going out.

I’m going to go nuts if I don’t make friends with some people closer to my age and maturity level while I’m here. I don’t have any regular activities, since I am here on my own doing research, not taking classes or working. Does anyone have any ideas for how to meet people around here to hang out with? I speak excellent French, but Parisians are pretty insular and it’s hard to worm your way into their friend/acquaintance circles.