Eddeboe, Archaeological site in Flensburg, Germany

Eddeboe is an archaeological site in western Marienhölzung in Flensburg with two distinct fortified areas structured by walls and ditches. The remains of a former fortified residence are visible there, with ground plans and water features still evident today.

Two medieval castle sites lie in the Marienhölzung. The older, on the Brandplatz, was a rectangular water castle about 70 by 45 metres, surrounded by a moat fed by a stream. The younger castle, on the Junkerplatz about 100 metres west, measured roughly 150 by 130 metres and was ringed by an earthen rampart and ditch. A parchment letter of 27 March 1401 names Ivar Juel as owner; the family Jul is linked to Flensburg's first mayor, Peter Juel.

The name Eddeboe translates as "ancestral seat" (boe = castle, Edde = lineage). According to Diplomatarium Flensborgensis, the family Jul held the estate, and Peter Juel, named there as Flensburg's first mayor, came from it; a parchment letter of 27 March 1401 names Ivar Juel as owner. Legend tells of a wild knight of Eddeboe who abducted girls, and of a sunken castle whose tower tips and bells are said to appear in the Jungfernsee at noon.

The site is accessible and features an interpretive panel on-site with explanations of its history and structure. It is best visited on foot from the city to enjoy the surrounding forest setting.

The complex was built on a hill and surrounded by water ditches, making it stand out markedly in the flat landscape. This location provided protection while simultaneously displaying the owner's wealth and power to all who passed by.