Take a sightseeing tour in Porvoo national urban park with Hop-On Hop-Off Bus Rinkeli. The city offers a Hop-On Hop-Off Bus for locals and visitors during 18th June - 2 Sep 2018, Mon-Sun 10.45 am - 1.15 pm and 1.45 pm - 3.45 pm. The tour takes about 30 min. Hop-On Hop-Off Bus Rinkeli is free of charge. Follow the bus and route here.
The bus drives all the way to Sikosaari island where you can find a nature trail and a bird watching tower. You can stay here and enjoy the nature and return back to the center by foot or by catching a later bus.
Find Rinkeli timetable here and route with bus stops here