Scenic route from Helsinki to Naantali?

Terve!

I'm planning to visit the Moomin World with my family this summer. Since we're Estonian and coming via ferry, that involves driving from Helsinki to Naantali. However, I think that driving on a highway for the entirety of your road trip is a bad way to see a country and I'd much rather see the countryside. If it adds a few hours to the trip, so be it.

Does anyone have suggestions on which roads to take, what to see on the way?

Kiitos!