Pulvermaar, Volcanic lake in Gillenfeld, Germany.

Pulvermaar is a volcanic lake in Gillenfeld featuring a circular basin surrounded by steep funnel-shaped sides. The water reaches depths of around 72 meters across a diameter of roughly 700 meters.

This lake formed during the last ice age roughly 20,000 to 30,000 years ago when magma encountered water-saturated rock layers. The explosive interaction created the funnel-shaped depression that now holds water.

The Pulvermaar belongs to the Gillenfeld maars, together with the smaller Holzmaar. Its name is not explained in the sources; what visitors notice today is the bathing place on the eastern shore, the only developed spot on the almost circular lake, while a footpath runs through the beech forest on the crater rim.

A footpath runs around the lake through the beech forest on the crater slopes. A bathing place sits on the eastern shore. The area around the Pulvermaar, the Römerberg and the Strohner Märchen, about 110 hectares, has been a nature reserve since 1984.

The crater was originally about 200 metres deep, with a rim of ejected material some 50 metres high; the lake now holds roughly 1.2 million cubic metres of water. Underwater terraces and ice wedges in the tephra layers led researchers to date its formation to the last ice age, 20,000 to 30,000 years ago.