We did the hike from Osterbo (where we stayed overnight) to Vassbygli in July with my husband and two teenage girls. The weather was dry so we chose a bit more difficult route via Bjornstigen. The views from there were impressive - I highly recommend - but the descent is steep assisted by metal wires so it would be challenging if the rocks were wet and slippery. The river and the waterfalls are very beautiful. We returned to Osterbo by local bus. There were many hikers so we did not fit to the first bus but had to waite for almost an hour for an extra bus. We made the hike via Bjornstigen in 5 hours but had to waite for bus for two hours. Luckily there is a kiosk at the bus stop in Vassbygli where you can buy drinks and snacks and even have a shower.