First and foremost, as a Scandinavian city, Helsinki is very expensive. If you are only spending a day here, you have an option of bringing your own food along. We brought food during our day trip from Tallinn, which ended up far cheaper than buying food in Helsinki.
If you arrive by cruise from Tallinn or Stockhom, head to see the Uspenski cathedral.
If it’s summer, from Kaupattori ferry terminal take the ferry to Suomelinna. It costs 2.50 EUR one way. You also have another option JT line waterbus, but this costs almost double.
Suomelinna island is beautiful. Follow the main path from the beginning, but after you cross the small bridge from one island to another, head to the west shores of the island, there are very pretty parts and you can take great pictures and enjoy watching the sea. In the end, you will end up at the King’s gate. To come back to Helsinki, you will either have to go back to HSL ferry to where you landed or you can take the JT line from King’s gate.
Head to the Senate square and Helsinki cathedral. The cathedral is free to enter. Keep in mind that it’s not open 9 to 6, as most websites tell you, but closed at times. When we were there it was closed from 15.00 to 16.45 for instance.
Have coffee at one of the wonderful local cafes. We really loved the atmosphere and coffee of Paulig Kulma. We relaxed in their hanging chairs upstairs before heading back out to explore. Another great coffee shop is the chain called Espresso house. One branch is near the Helsinki cathedral, but there are several around the city.
If you are interested in Finnish art, explore Ateneum museum. The building is very interesting. It’s extremely expensive though – 17 EUR.
Check out the building of the National museum of Finland housed in the old church.
Head to Temppeliaukion kirkko – a Lutheran church built in stone. As Helsinki cathedral, this is also closed at times for weddings.
Take tram. The trams in this city are great. You can take tram #2 from Senate square to Temppeliaukion kirkko.