Erlkron, Tower ruin in Glücksburg, Germany

Erlkron is a ruined tower built in 1900 by Heinrich Haß on a hill above the Schwenau valley, using stones from the demolished Duburg in Flensburg. It has pointed-arch window openings at different heights and a Gothic-style balcony. A platform in front and a tower room offer views of the valley and the Ox Islands in the Flensburg Fjord.

Heinrich Haß, a veteran of the 1870–71 Franco-Prussian War, built the artificial tower ruin in 1900 in his garden on a hill above the Schwenau Valley. He used handcrafted stones acquired when the last remains of Flensburg's Duburg ruin were demolished at the end of the 19th century. In 1960 the Zellermann family bought the property; the tower was restored and later placed under monument protection. Around 2000 the masonry subsided and was repaired, without rebuilding the original battlements.

The name Erlkron's origin is uncertain. It may derive from the alder carr woods (Erlen-Bruchwälder) of the Schwenau valley, or from the Danish ellekonge, literally "elf king", which German rendered as Erlkönig in the ballad. Danish elletræ means alder, while elle also means elf; Kron may echo Krone, as in Kronborg.

Visits are arranged by agreement with the owners rather than at fixed opening times. A viewing platform stands in front of the tower, and the tower room can be used for a rest; in good weather the Ox Islands in the Flensburg Fjord are visible from there. The ruin is also recognizable from the bridge of the former Schwennau campsite, closed in 2016.

The landscape garden surrounding the ruins hosted an exhibition in 2009 featuring stone sculptures from Zimbabwe alongside paintings by Jürgen Zellermann. This artistic use brought contemporary work to a historic site.