Burg Freienfels, Medieval castle ruins in Freienfels, Germany.

Burg Freienfels is a medieval castle ruin positioned on a hilltop above the Weil Valley near Weinbach in Hessen. The remaining structures include defensive walls, a central tower, and stone foundations that reveal the original layout of the fortification.

The builder and construction year are unknown; it was likely built by Count Heinrich von Diez-Weilnau in the late 13th century to block Count Adolf von Nassau's expansion. First documented in 1327, when Siegfried von Runkel bequeathed the mortgaged castle to his nephews, who sold it that same year to Count Gerlach von Nassau. In 1466 the dilapidated castle and village passed as a Nassau fief to knight Johann von Schönborn, whose descendants held it for nearly 250 years. Never destroyed in war, it was abandoned to decay in the mid-18th century and used by villagers as a quarry.

The name Freienfels refers to the rock spur above the Weil, and the village below grew alongside the castle. The counts of Nassau acquired the pledged stronghold in 1327, ending its role as a rival base. The von Schönborn family held it as a Nassau fief for almost 250 years from 1466, and their descendants lived in the complex.

The site is reached by a bridge over the roughly 20-metre-wide neck ditch, leading directly to the gate; the earlier approach ran up a steep path from the Bornbach valley. The tower was made walkable around 1910, when the whole ruin was opened to the public. The courtyard is split into two levels by a north-south terrain step, so expect uneven footing.

The castle was never destroyed by war or feud; its decay came when villagers used it as a quarry for house building in the mid-18th century. Around 1907–1908 Berlin architect Bodo Ebhardt drew plans to convert it into a Wilhelminian villa, never built.