Any and all of the above sound like fun, and many are not mutually exclusive. I'm rather fond of the visual of high tea followed by bubbles in the park, but that's just me :)

Ride/tea/dance/hottub depend upon how many and who you want to be involved (more limited #'s and/or not everyone is able to do all of those things). Park allows more to play, but is more open-ended, which you might not want.

As Raf said...it really depends upon what else you want from your party.