This 100m long wall, dedicated to your self expression, is located in the old industrial port area of Suvilahti. One of the few places in the city where graffiti is not illegal, indeed it's actively encouraged.
Worth checking out even if you don't personally want to add your tag. It's a really vibrant piece of live art and culture in the city and you'll definitely meet lots of young, interesting types down there if that's what you're after.
Bring your own spray cans.