A WONDERFUL PLACE !! I 100 % recommend Casey's flat to anyone.
The flat is very nice, clean, cozy, charming and extremely well situated only 2 minutes from the tube (going both east and west in Oslo) buses and tramway in addition to be very close to many restaurants, cafés, tourist attractions and shops. Oslo is not a very big city, you can discover most of the town by feet. The Vigelandspark, the park with the Royal Castle and the famous harbour "Aker Brygge" with shopping, museums and restaurants are all in walking distance from the flat (or short away by tram).
I must also add that the bed is defintively the best we have ever slept in. Heavenly!
We stayed 4 days in Oslo and the whole week-end was lifted by Casey's great place.
We will definetively come back :-)