The easiest route is to take the tram from just outside the hotel, line 17 or 18 towards Rikshospitalet. Depart at Universitetet Blindern.
Walk through the campus until you get to the main square. Georg Sverdrups hus is the tall building to your left.
You may also walk 8 minutes to the Nationalteateret station and take the subway. Take line 3 (Sognsvann), line 4 (Ringen) or line 5 (Storo) westbound, to Blindern station. When you leave the train, walk up the hill and cross over the first street (Problemveien). Continue walking in the same direction. Georg Sverdrups hus is the first tall building in front of you.