I think from early to mid-2000's there were lot's of demonstrations in Helsinki. Maybe there are still many organized, but with a smaller scale and I don't go to them anymore. Some people may say "maybe you have grown up, and that's the reason you don't go anymore" (this is very Finnish way of zeroing everything). I still think it is just my lazyness I don't join demonstrations anymore.
SMASH ASEM-demonstration was probably the craziest demonstration I've been involved in Finland. All the demonstrators were surrounded by riot polices for several hours in the cold central Helsinki. They didn't allow us to leave the area, not even to restroom. They were just waiting that people would do some huge act, but hey, this is Finland. People act very calm always (except when they are drunk).
I took this photo in ASEM-demonstration. It tells a lot.