Rocknen is an esker roughly 2 kilometres long and flanked by broad areas of marsh on both sides. It is home to old-growth pine forest and is a refuge for twinflower (Linnaea borealis). A path runs along the top of the esker and offers a good view of the area and Madsjön, a small lake, to the east.
In the marshy areas, bog asphodel is more plentiful than anywhere else in Småland. Breeding birds include the common crane.