Next to Helsinki there is an old fortress island called Suomenlinna. It is a UNESCO World Heritage site and very lovely place to go for a walk. You can walk around the island in few hours. There is many very old buildings and remains of huge old stone walls. There is also few restaurants, cafeterias and even a Japanese tea room. You can take a ferry from Helsinki market square. Ferries come and go every 20 minutes during summer and every 45 minutes in winter. Ferry ticket is 3€ and it is valid for one hour if you want to have just a quick visit.
