The city center is quite small, and you can walk around it if you want. Here is just a tentative tourist route around Helsinki, which will allow you to get to know the city in 4-5 hours:
1. Start your walk from the Station Square (Rautatientori) - it is one of the most striking examples of Scandinavian style in architecture. Next to it you will see the Finnish National Theater, which resembles a fairy-tale castle.
2. Pass through the square in front of the theater and you'll find yourself at the Ateneum, Helsinki's National Gallery. Here you'll find an excellent collection of Western art from the 18th to 20th centuries. Walk around the gallery and you'll come to the next leg of your Helsinki itinerary, Universitetgatan (University Street).
3. Walk two blocks and you will see the National Library on your left hand and Senate Square with the Helsinki Cathedral as the main symbol of the city in front of you. The Helsinki walking route should continue along Alexander Street, a neighborhood of Swedish mansions of the XVIII century.
4. Next, the Helsinki walking route goes to the Katajanoka Canal - orient yourself to the golden domes of the Assumption Cathedral (it is the largest Orthodox church in Western Europe). Here, surrounded by birches and junipers, we suggest to finish the hiking trip.