Though our summer trip through Scandinavia pit stopped through a lot of cities from Stockholm to Tallinn - our main stay was in the smallish city of Tampere in Finland.
Though considered one of the biggest and most culturally important cities in Finland and even surrounding Scandinavia (after Helsinki, of course) Tampere felt extremely small, pleasant, and relaxing to me - and was the perfect place to use as a hub to visiting other parts of Finland and Estonia.
A beautiful little city - with lots of great architecture and some wonderful shopping districts, it's very easy to spend several days just wandering the streets and getting a feel for life in Finland. You are more likely to stumble across people who speak a bit of English in the city than you are in the smaller towns surrounding it - but as with everything in Finland it's good to keep your fraise book handy. Especially when food shopping - had we not had a local friend there to help us, we would certainly come home with a lot of strange food! All this, though makes for great travel stories - and I highly recommend you try some local 'makara' (sausage) while you are there.
The summers in Finland can be surprisingly warm, though unfortunately we seemed to have chosen the one summer every 6 or 7 years that is a constant downpour. Still - when the sun did poke out and we were free to wander pleasantly down the back streets and parks of Tampere, it was beautiful weather, and we spent a large amount of time taking photos of local monuments and statues (of which there are many) and enjoying ice cream bought from a local vendor.
Tampere is well known for its cultural life and many art and film festivals. Through out the spring and summer the city is often visited by both film and music festivals (check out the cities website for specific festival dates.)
The location of Tampere is also very good for the traveller - as it is in the southern part of Finland only about an hour north of Turku (a large port for those arriving by boat from other countries) or about two hours north of Helsinki.
I highly recommend the bus system in Finland if you need to travel around. The road systems are very good, and very straightforward if you choose to drive (much more like American roads than other European countries I've been to.) but the buses are very efficient and comfortable - if a bit more pricey than you find in other countries.
Be sure to bring your student card if you are a student. There are many large discounts available for those who are still studying.
Big enough to have plenty of food, nightlife, culture, and shopping - and still small enough to feel pleasant and inviting - Tampere is a pleasure to visit, and a great place to stop in on your way through Finland.