There is a new pop up cafe Hauskafe in Lasipalatsi that you really should try. It is Helsinki's first time café. The concept already exist in some other big European cities and now also came to the Finnish capital.
Instead of paying for what you order you pay for the amount of time you spend here now. When you enter you receive a card marked with your entrance time. Every hour costs 5 €. During the time you spend you can have as much delicious Johan & Nyström coffee, tea and cookies as you like.
You can also play table football, board and cosole games, read books or use the meeting room. Some special cakes and sandwiches are charged extra but still for a rather reasonable price. You can also bring your own food or beverages if you like.
For now Hauskafe will be at this location until mid December. If things go well, the cafe will be established there permanently.
Give it a try!