There are many hotels and other overnight offers in Oslo, via

We recommend to stay hotel around National Theatret station (Nasjonalteatret in Norwegian), for metro, tram, bus and train. On the other hand, Oslo center is not big, so you can stay at many other hotels with only a short trip to the venues.

Reasonable places:

Google map for hotels in Oslo city center,10.7361862,15z?hl=no