Thanks for your help. She's off on her date. We had an argument about shorts being too short (I won) and it kind of side tracked us from our goal of figuring out what she was going to do so your suggestions are very helpful. Biopark was one of her first thoughts, but they close early. Tuesday is not a good night for a first date. She "thinks" she's too cool to be goofy, so bowling was out. I think mini golf might have won out.
OK, so having looked over the post I linked to, I see there's not a lot of good stuff for 18-year-olds.
The biopark is always a great choice. The gardens are neat and interesting and present lots of opportunity for bringing up background info and personal knowledge, whether the beauty of the plants inspires you or the biology behind them or even watching the other people in the park.
Other opportunities that offer the opportunity for conversation are best. Eschew plays, movies, and other events where you sit next to each other in the dark.
Mini golf, bowling, and other "goofy" sports are good, too; you can laugh at your own ineptitude.
I figured I would throw in. Being that she is 18, and this is her first date, I would stick to something fun and relatively social. Maybe go find some good putt-putt and then hit up a coffee shop for some conversation. Basic, but a good summer event that doesn't bring a whole lot of pressure to the table.