A map of the Lahnstein forest.

The Lahnstein forest is a forest with more than 10,000 hectars in size, around castle Königsbrunn. It belongs to the Lahnstein family. In late 2010, the Lahnsteins decided to use its resources and deal with wood in a new company, Lahnstein Enterprises, after the Lahnstein Holding fell into the hands of Tanja von Lahnstein. They soon found a contractor from Japan, Yakamoto. Eventually they hired a new forester in 2011, Thomas Wolf.

Because Ansgar von Lahnstein wanted to see Lahnstein Enterprises go bankrupt, he set a fire in the forest, burning down much of it, which made it impossible for the Lahnsteins to complete the contract with Yakamoto, and so they were to pay a contractual penalty.

One of the oldest parts of the forest was Ostforst, where one of the oldest trees was planted, the Lahnstein Oak.