Been there twice last few years. First walk around town, see the old town (gamla stan). It is a bit of a tourist trap but a must see. The parliament, the palace, see the changing of the guards etc.
- Museum with a complete hundred of years old marineship: http://www.vasamuseet.se
- go to Skansen (park and rest of the island (djurgarden)): http://en.wikipedia.org/wiki/Skansen
- take a look at the stockholm card. Gets you free access/reduced prices to alot of things, and free public transport.
- also i heard that sodermalm is quite nice, although i do not know much about that part of the city.
- watch Swedish woman. Those genes are pure gold i tell you
Being 17 the rental car is gonna have to wait a few years. I'll get one of those cards for sure, and i'll check out that museum. sodermalm is something i've also heard about. will go there. I'll try and see some ladies too. Should be nice out when i'm there so i'll take advantage of that too.