If you would like to get to know the Finnish nature, I would recommend you to visit Haltia, the Finnish Nature Centre in Espoo. It is only a half an hour ride from Helsinki by car. Though it would be only the second best place to visit, right after the real nature itself.
We visited it some time ago with my family, and my littles one fell in love with the video installations that covered not only the walls but also parts of the floor. Meanwhile my four year old enjoyed crawling into the dark fox’s and bear’s dens. For the adults the place has more to offer, than what it seems at the beginning. I recommend to read more on the building itself. The centre is designed by Finnish architect Rainer Mahlamäki and it is the very first public building in Finland made completely out of wood. It is also very ecological, as they for example produce over 80 % of the electricity needed by themselves. Take a while to look at the Osmo Rauhala’s peace of art where swans play the game of life. It makes you see the beauty and the randomness of life.