Mattheiser Wald, Protected forest area in Trier, Germany

Mattheiser Wald is a 447-hectare nature reserve in southeastern Trier, covering most of the former Feyen and Castelnau barracks training ground. It is an old-growth oak-hornbeam mixed forest in the Aulbach valley and adjacent slopes, with ponds, open patches and visible remnants of military use such as firing positions, training courses and tank roads.

The forest belonged to the St. Eucharius–St. Matthias Abbey until secularisation, then served as a military training ground, from 1938 for the Feyen/Castelnau barracks and later under French use. During the Cold War a special weapons depot stood in the forest under French guard. After the French withdrawal in 1999 the area became conversion land; it was placed under nature protection in August 2003 with 447 hectares and recognised as an FFH area from mid-2004.

Locals and visitors use this forest as a retreat where they walk among trees and meadows to experience the natural surroundings near Trier. The paths guide people through different habitats that help them understand the area's living landscape.

Visitors can use two marked circular routes to explore the forest area at their own pace and move between different sections. The paths remain walkable throughout the year, allowing a visit in any season.

The FFH designation is not a separate management category but part of Natura 2000, the EU ecological network; Trier listed the area as an EU-recognised Fauna-Flora-Habitat site from mid-2004. A support association founded in May 2004 pushed for protection and dissolved in 2008 after its goals were met.