Ideas off the top of my head:

group party at Blindekuh restaurant in Zurich (done this, great fun)

parties at juckerfarm near griefensee, where they put on farm competitions (done this, great fun, all ages)

do a search or look at brochure for "team events" on myswitzerland.com

apero and private party in one of the animal areas at ZH zoo.ch or dinner at the private restaurant overlooking masoala hall (done both of these, great fun)

private group party in secret bunker of historical pinball machines (done this, great for surprise, everyone loves it, not too expensive, great Zurich secret)
http://www.outlane.ch/

Lightheard BoccioBall lesson, tournament, food afterwards in BoccioDromo in Altstetten next to Letzigrund stadium (fun, easy, all ages, good instructors, fun to try, above italian restaurant with plenty of room to host parties)

sushi cooking course (done this, does great job)
http://www.sushifusion.com/en/cooking.html

other cooking courses: (done this, does great job)
www.laughinglemon.ch

Get group Square dancing at party:
http://www.squaredance.ch/de/Allgemein/willkommen.php

have party in huts in forest:
http://www.zueriwald.ch/Thuetten.htm

community centers to hold parties
http://www.gz-zh.ch/home/index.php?gz=0

rent an exotic car:
http://zurich.angloinfo.com/af/469/z...le-rental.html

Boat party on Lake Zurich

Curling lesson, fondue dinner, drinks afterward at Dolder IceRink on Zuriberg (done this, easy, great fun)

attempt at bodyflying at center in direction of ZH airport

-MakeABigWish

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