Ferry Fjord Ride
This is a cool experience. They ferries are cheap (people are not paying, cars are ~3Eur). Would recommend if you fly from the outer airport.
Sandefjord
Ghost city. Literally there is no one in the street and everything was closed at 5pm. Skip.
Drøbak
Although we found cute little bakery for coffee and burek, apart from that this small town has nothing to offer. Only expensive parking :D