We had a great stay at Marthe's apartment. It is a beautifully designed apartment and we loved every inch of it. It's a bit small, but it was eventually fine for the four of us. Just don't bring large luggages. We didn't get to meet Marthe, but check in and check out were easy. The location was perfect, very close to the Royal Palace and the city centre. Definitely this recommend this apartment for your stay in Oslo!