Destroyed in 1943 during the aerial bombings of World War II, provisional reconstruction began in 1950, at which time it adopted the temporary name of Lower Saxon Homeland Museum (Niedersächsisches Heimatmuseum).

[de ] In 2013, discovery of significant medieval finds during construction work on a neighbouring plot led to a three-months archaeological investigation in the area.

Incorporating the Beguine Tower and remnants of the ducal armoury, the building by architect Dieter Oesterlen features a polygonal footprint around a pentagonal inner courtyard.

Its striking façade of three storeys with alternating broad sandstone surfaces and narrow bands of windows has a staggered appearance when seen from its north along Castle Street.

A light installation dating to the year 2000 by the American conceptual artist Joseph Kosuth of an illuminated quotation by Gottfried Wilhelm Leibniz on the building exterior facing the Leine reads:[8] There is no desert, nothing infertile, nothing dead in the world, no chaos, no confusion, except an apparent one, something like what you would see in a pond if you saw a confused movement and a swarm of fish from some distance, without distinguishing the fish themselves The museum is divided into four departments: The museum has one of the largest photo archives in Germany, holding around one million historical photographs for consultation and acquisition of reproductions.