We were very lucky to be “upgraded” to a three bedroom flat with a large balcony - it was very central near the Opera House and Oslo Sentralstation and various bus routes. We tended to cook/eat in with 2 supermarkets less than 5 mins away - for those wanting to eat out there are PLENTY of restaurants!
The facilities were outstanding and the bed extremely comfortable. I could not recommend this highly enough to anyone wishing to stay in Oslo. In summer bring your swim wear as they are several sea swimming options nearby.