Gjøvik Olympic Cavern Hall is the town's oddest and best sight: an ice arena built inside the mountain for the 1994 Winter Olympics. From the street it looks almost understated, then the entrance drops into a huge blasted-out chamber where ice hockey, concerts, and local events take place under rock.
It is worth seeing even if nothing is on. Norway has plenty of grand landscapes, but few towns can show you an Olympic venue hidden in a cave within walking distance of the centre.