@cher99840, the path that I took had a couple of difficult rocky creek crossings, one where a rope was provided to assist walkers if the level of the water rises. This is on the Gudbrandsdalen leg of the way from Oslo to Trondheim. There are many different variations to St Olav's Way, not just the major route (and its variations) from Oslo. If that is what you are planning, the major stages, as I saw it, were
- Oslo to Lillehammer - this is largely open farmland, although there are days walking through pine forest, upland lake land and summer farms (saeter). You are never far from Lake Mjosa, but you won't always realise that.
- Lillehammer to Dovre - here you would be walking up (and down) the sides of a glacier formed river valley, the Gudbrandsdalen. It starts as farmland each day on the valley floor, with pine forest, summer farms and abandoned crofts further up the hillside. There are steeper climbs here, particularly around some of the ski resorts.
- Dovre to Oppdal - crossing the Dovrefjell. Desolate upland valleys, former military training areas (they never train in the nice places to visit) and summer farms and then winter farms closer to Oppdal. Some really magnificent country to walk in.
- Oppdal to Svorkmo - another complex of river valleys, with a bit of hopping across into the next valley. Generally less going up and down, but it won't stop until you get to Trondheim.
- Svorkmo to Trondheim - could be divided, but generally now in upland marshes and then farmland around the fjord. Some forests, less elevation gains but still some individually difficult short stretches.