What to see in Ostfold near Sarpsborg?

[friikadello]

Hello!
I'm kinda new in Norway, I live in Sarpsborg. There is a friend comming over for a couples days.
During the weekdays I will be working starting 16.oo but before that I want to show around, but I dont know anything much here. As I will have to work for the second half of the day, we can't go too far. We both come from Latvia.. It's absolutely flat country, our highest mountain is 316m high. As it's gonna be her first time traveling out og the country I really would like to show her Norways nature, it's inceredible comparing to what we are used to.

Places what i'm thinkng to take her to.

Søndre Jeløy - Albby .. Love that place
Vigelandsparken - Havent been there myself, looking forward to it.

Halden - never been there myself, but looks like a nice place where to have a nice walk around the castle and grab some coffee

Kjøkøy / Kråkerøy (That's how we call that road #108, for us it seems so surreal and unusual)
Ofcourse we will have a couple hours in Oslo, Kings Castle, Opera house ( don't know anything much there )

I will have day off on Saturday, thinking to take her to Kongsberg for skiing and to see more of mountain landscape.

I would appreciate any other ideas and suggestions for Must See or Visit in this area. If not for this week, then in future plans