A 4-Day Trip to Finland

I’m going on vacation to Tallinn, and then taking a ferry to Helsinki. Where would you recommend going from Helsinki to really experience the Finnish atmosphere and see nature? It has to be accessible from Helsinki, since I won’t be renting a car. I’ll have about 4 days in Finland, so I was thinking of either exploring Helsinki in one day or possibly skipping it altogether. What would you recommend? Thanks in advance for your help!