Not the biggest but the tallest waterfall in Sweden at 93 metres, 70 of them free fall. In summer you can climb and walk along a path up to the top of the canyon which is wonderful even though you almost get this urge to throw yourself off the cliff and there are signs warning you. In winter, people come here to do ice climbing at the fall but there has been deaths and you have to really know what you are doing. Not even the expert ice climbers can always tell what the ice is like here, it's always that unpredictable. Below the falls is also a Naturum, Swedish Environment Agency and Dalarna County's exhibition on local flora and fauna.
As you walk around the waterfall, all sorts of tree shapes can be seen. All adapted to the harsh fell climate and maybe growing sideways rather than tall...You also get to see the difference between the forest valley below, and the windy plateau. Unlike many other fell plateaus, this is off the limit for reindeer herding and so, you will find much thicker lichens on the ground here than elsewhere. Up here you have 140 kilometres of marked hiking trails - some taking you towards Norway.
Many people think all forests with big trees are ancient but in fact, even in a forest country like Sweden, it's only a few that can really be called ancient. One criterium is that nothing should have been done to it but it must have been left so that trees start a natural decomposing process, beetles and woodpeckers thrive etc. This is one such rare ancient forest in the valleys below the waterfall canyon.
This is far from the nearest bus stop. Your best bet is to drive to Särna (which you CAN reach by local bus) and north of it, follow the road to Mörkret. It is around 6 kilometres between Särna and the park so if you plan to hike, a taxi is viable. If you check with Dalatrafiken, you might also be able to arrange taxi transport through them as you can often arrange things with local transport companies in remote parts of Sweden.