Heidenhäuschen, Cultural heritage monument and summit in Hesse, Germany.

Heidenhäuschen is a multi-peaked ridge of the Upper Westerwald in Hesse, reaching 397.9 m above sea level and rising up to 200 m above the Elbbach valley and the Limburger Becken. It is built mainly of olivine basalt from eruptions about 28–22 million years ago, and two former volcanic craters have been identified. A field of basalt boulders formed largely under ice-age conditions near the top.

Archaeological finds near the ridge include a stone cist at Niederzeuzheim from around 1900 BC and burial urns from about 1000 BC. For the Hallstatt period (about 700–450 BC) ramparts are documented at the summit, and during the La Tène period the Celts laid out several ring walls, with two coins minted by the Treveri found here in 1902. The Ubii later held a court on the hill dedicated to the Matronae Mahalinehae, which continued as a Frankish court and was moved to Ellar in the Middle Ages.

The name comes from the old Germanic legal term harahus, a site where oaths were sworn; the dialect form hârehäusje was reinterpreted as Heidenhäuschen in the early 19th century. The Ubii held a court here dedicated to the Matronae Mahalinehae, and the surrounding area is still called "das Gericht" locally.

The summit can be climbed from every surrounding village, including Ellar, Hintermeilingen, Steinbach, Oberweyer, Oberzeuzheim and Hangenmeilingen. The Westerwald-Verein's long-distance trail IV (Fernwanderweg IV) passes directly below the top. The hill lies about 11 km north of Limburg an der Lahn, between the Elbbach valley to the west and the Limburger Becken to the south.

The name comes from the Frankish legal term harahus, a place where oaths were sworn, preserved in the dialect form hârehäusje and reinterpreted as Heidenhäuschen in the early 19th century. The surrounding area is still called "das Gericht" (the court) locally.