Being a Finn myself I have to agree with the above. Must be a nice place to visit ! :hiclp: And a stay of 2 weeks at least may add a possibility of good luck with the weather too.
We are at the moment experiencing a whole week of 30 degrees Celsius and sunny weather throughout the whole country but you never know - it could turn to 14 and rainy. Btw, the mosqitos and midges need moisture to breed. So being as dry as now, not much of them around.
And speaking about the lakes. There are hundreads of thousands of them. Small ones around the Helsinki area, and more lakes than land in some parts of the country in east... just look at the map.
On the other hand, the coast of the sea is a totally different nature with a very exceptional archipelago. From Helsinki I would recommend to take a cruise from Kauppatori (market place) or at least a boat to Suomenlinna. http://www.suomenlinna.fi/en/
An old fortress island just outside the city.
If you want to experience nature in forest, (which I do recommend too) there is a national park just outside the city area with marked hiking paths in different lengths too. http://www.visitespoo.fi/visitors_guide/enjoy/nature_experiences/nuuksio_national_park
Sorry about the overflow outside the glass subject... just in case there would be a day or two for something else than shopping...
About the museums, yes you can google "lasimuseo" (glassmuseum) + riihimäki, nuutajärvi or iittala. Definitely a must, all of them.
Also Arabia museum is an interesting place to visit: http://www.arabianmuseo.fi/web/museumarabia.nsf/pagesbylevel/ENG0?OpenDocument&LANG=ENG
A lot of shops and links to shops etc. listed here http://www.antiikkilinkit.com/indexal.htm
(you may want to use google translator
Feel free to ask if you need help.