Party Ideas?

[CouldaShouldaWoulda123]

Hi,
It is my dd's 15th birthday soon and she has decided she would like a big party as her present but would like it too be really memorable!

She is quite interested I the idea of a sleepover in an unusual place but is not sure where!

So mumsnetters, any ideas!

Alton Towers have a sleepover room which sleeps 6, looks amazing but assume it's quite expensive.

Do you have a budget in mind?

Some of the museums do sleepover nights.

What about one of them Yurt type things?
Some places also do tree houses to hire out but i think they are pretty pricey.

Can you borrow/ rent a field , hire a ports loo, put up a massive tent to hold a party and have them all bring tents to have a camping party. Lots of music from iPods. If it rains they are undercover. They would love it.