15th birthday party ideas?

So my birthday is in early May and I live in San Francisco. I want this [arty to be unique.. not just a dinner party or a swim party or especially not a bowling party. Please nothing to expensive, and what my idea was is to have a big party, and then maybe hang out downtown with them and then have girls go home and rent a hotel room for my friends(or maybe just go to my house for a sleepover). (and hotels cost a lot +food) so the bigger party can't be to expensive. And keep in my transportation, cause i can only fit 8 people in two cars not including my parents so it cant be to far from the hotel.