Yup yup. Just bring it up. If you want to be smooth don't be all, "Hey, do you like doggystyle?" haha.
I always start by bringing up a funny or crazy story in my life that somehow has to do with sex.
Like the time my ex gf and I got caught doing the do in a park by a jogger.
I'll bring up something about nature and we'll shoot the shiet and that will get onto the topic of parks. Then I'll start talking about how one time I fell off the playground equipment cause I was stupid and did a crazy dare. If she doesn't volunteer a story about something stupid she's done I'll ask if she ever fell off the swings or some shiet. A few minutes later I'll be all, "Oh man, here's a pretty crazy story. It was embarrassing as hell at the time but now it's just funny. Anyway, my ex gf and I decided to go to the park one day cause it was nice outside...".
Easy peasy. And that's just one of the many, many, ways to bring it up. But ya know what? If you're really having a great time with the woman, playing it cool, making her chase you, etc, SHE WILL usually bring up the topic of sex first.