Traveling is fun.. as long as you can afford it. So why not make it affordable? In cities like Paris, London, Edinburgh and Helsinki you know you are going to pay a lot for your stay your food and transport.
While most people go to Tallinn for one day from out Helsinki, I did it the other way around. I booked a stay of three days in Tallinn, but because that is a relatively small city I decided to spend one of those days in Helsinki.