Thon Vika Atrium: Budget, almost on the waterfront

Three minutes to Aker Brygge. Eight minutes to the Nationaltheatret train station, which connects directly to the airport. A bus stop right outside. 

The building wraps rooms around a central atrium. Rooms facing the interior get their light from the atrium. They're dim. Ask for an exterior-facing room when you book, or you'll spend the day in a cave with a fridge and a Chromecast. Standard rooms run about 16 square meters, this is tiny even for Oslo standards. Two people with suitcases will be doing a shuffle dance around the bed.

The breakfast in the Holmen restaurant is outstanding. Big spread, good quality, proper hot options. Free coffee and tea in the lobby around the clock.

The staff are sharp and helpful. The neighborhood is upscale waterfront, restaurants everywhere, quiet enough at night if you're set back from the main drag.