Maybe a complicated puzzle treasure hunt?
Clues that lead to more clues.
Maybe get some nerf-guns, and paint them steampunk style, and have a gunfight
Croquet
You could build a "base camp" using some sheets to make a tent, and serve high tea in it.
Use google to find ideas
http://www.pinterest.com/christinestrena...
http://toastpop.com/ideas-for-a-hosting-...
http://www.thesteampunkempire.com/forum/...
My 17th birthday is coming up in the next week and I have a general idea of decor and food revolving the Steampunk theme. No, people aren't going to dress up. There's going to be a max of 8 girls coming, so it's not /huge/.
My backyard is a good size but only dirt and rocks, but I would still like to use it in a way? I can go into also every area of the house except for the bedrooms. I can also probably sneak into the gated neighborhood to go into their park area (I used to live there). I also would love some ideas of what to do during the party. Yeah, there will be food, music, and people, but I need to plan some sort of games for us to do. We're not a 'girly-girl' bunch, so something fun, active, and a little crazy would be perfect.