Wonderful flat with nice views across the old town. It has excellent public transport links. We can recommend coffee on the balcony with fresh cooked cinnamon rolls. Watching sunsets and sunrises there is also a delight. The flar was a perfect size for two. The closest large shop is across the church yard.
There are great views from the Ekeberg sculpture park and "the scream" location (famous from the painting) up on the hill opposite the flat. If you like walking, then many of the metro lines finish in the hills, e.g.: Frogneseteren, Sognsvann and Grorud, and there are woodland cafes that can be walked to easily (5km) for a waffle and a hot drink.
The Viking Ships museum is worth visiting, and it also gets you access to the Historic Museum (within 48 hours). On the same headland as the Viking Ships museum, the Folk Museum is excellent, with many examples of traditional Norwegian buildings displayed over a wide area.
The Ruter app is the easiest way to use the public transport, and either single tickets or day/week tickets can be purchased quickly. It does not work on the ferry to the Viking Ships museum, it must be noted. The left luggage lockers within the central station, while a little difficult to find, are really helpful if your flight and check in time don't quite match up and you want a last day exploring.
Thank you, Niklas, for a great stay!