A huge and well-equipped converted warehouse circus school for children, amateurs and hobbyists and open training facilities for professionals during the day. The premises are available for rent or group booking for hen parties, events etc.
A huge long bouncy castle type airtrack, trampolines, tightropes, trapezes and more. They run a lot of regular classes, if you happen to be staying in Helsinki for any length of time. Keep an eye out on their website for open stages and other events. It's moving to Suvilahti, on Kaasutehtaankatu, as of January 2013.
Tuesdays from 9-11pm (apart from in summer) Sirkus Huima takes place - this is an open circus drop-in, free to all! Check out their facebook page.