In the Icelandic text Sögubrot af Nokkrum, Kolmården between Svealand and Östergötland is described as the border between Sweden and Östergötland (..Kolmerkr, er skilr Svíþjóð ok Eystra-Gautland. It also appears as Mirkwood in some editions of Sögubrot , in the legend of Helgi Hundingsbane and probably also in Völundarkviða.
Today the forest is traversed by the Norrköping–Nyköping railway, the Norrköping–Katrineholm railway, and the E4 highway, all connecting southern Sweden with Stockholm and the Mälaren region. Along the former there is also a Kolmården railway station, at the village of Krokek by Bråviken.
In 1965, the Kolmården Zoo (Kolmårdens Djurpark) opened close to this railway station. Being a well-visited zoo overall, the main attraction is the first Dolphinarium in Scandinavia, opened 1969, with a popular daily show (also giving name to the nearby basketball team Norrköping Dolphins). The dolphinarium opened during the spring that year with the new "Marine World". Since 1972 there is a Safari park in which you can drive with your own car. Since 1998 there is also Bamses Värld, an attraction devoted to cartoon character Bamse. The tiger house has recently been renovated and the elephants that belong to the king of Sweden are situated in Kolmården Zoo.