We’ve only been there on holiday so experience is limited. There is a Norwegian equivalent of Singletrack so might be worth a post on there. In our experience it can be tricky to find good stuff without local knowledge – big country, small population, and it needs a decent amount of traffic to make rideable trails.
We stayed around Hemsedal which was quite nice and alpine (just try and ignore the big ugly ski area). A local guy has signposted a few nice routes with some singetrack and quite a few technical rocky bits – but don’t expect a trail centre. They also included some minor roads / gravel tracks with toll honesty boxes (never worked out if cyclists were meant to contribute or not).
The outskirts of bigger towns and cities can be a good bet as people=trails – I know there is stuff to the north of Oslo. Think there is also something around Lillehamer area.
Mrs once did an XC world cup at Kristiansand in the south – that was in a parkland area on the edge of town but still brutally technical with lots of rocky features.
