Christianshavns Enveloppe

Christianshavns Enveloppe is a former system of outworks located in front of Christianshavns Vold and Stadsgraven, on Amager. in Copenhagen, Denmark. Its well-preserved, northern half is now part of Freetown Christiania and known as Dyssen. Its southern portion was removed in the first half of the 20th century and has now been replaced by a public park, Enveloppeparken.

Source: Wikipedia