Why not by-pass popular Helsinki and visit Turku, the ancient capital instead.? Turku is a compact city with many attractions, much of the focus being on its river and its attractive surroundings and walks.
For those who like Museums, Turku's castle is well worth a visit while there are other museums equally as interesting – enjoy an exploration of Turku's original past where ancient foundations can be seen under cover or the Apothecary's or Ship museums. All are within walking distance of the centre with its colourful daily open-air market in the Square. If you go in early August you will see the river crowded with the Tall Ships on their annual visit, many of which you can explore or perhaps see a re-enactment of a mediaeval city scene with a trial and mock execution. A variety of daily concerts are held in the ancient cathedral with others in the local Theatre. Close by you could visit the Waterloo cafe, converted from an original public toilet!
For a very modest cost you can take a tour of the Archipelago on board ship and partake of the sumptuous feast below during the voyage. There is also nothing better than a river trip to Naantila where you will find an attractive harbour lined with wonderful cafes and restaurants and mediaeval wooden-clad shops & houses. Across the bay lies Moominland, a paradise for children. The transport system is superb wherever you want to go and I recommend staying at a hotel just outside the city on one of the thousands of lakes for which Finland is famous. From Turku it is also easy to visit Stockholm in Sweden or Tallinn in Estonia on one of the many luxurious ferries.
In many ways Finland is well ahead of England with its transport systems, plumbing, department stores, hotels and restaurants. I have now been 8 times and find something new every time. Even its little local airport is a delight. Do go.