Whether viewed from the green, from the courtyard or from the park, Neuhardenberg castle is always the main focal point of the complex of buildings. The overall effect of the three-winged building's architecture is best appreciated from the courtyard.
The castle's architectural history began in the 1690s, when the estate, still called Quilitz at the time, was owned by Margrave Albrecht Friedrich von Brandenburg. He intended to build a grand manor house, but work did not progress beyond the cellar.
The building was not completed until 1785 to 1790, when Joachim Bernhard von Prittwitz erected a single-storey building with a huge mansard roof, an imposing central bay and an attic crowned by statues on top of the ancient cellar. The building's exterior was clearly inspired by the style of the baroque period. The interior, however, already featured some well-designed early neoclassical elements which have survived to this day. These were added by the great Prussian designer and architect Karl Friedrich Schinkel, an important champion of neoclassicism, whom Karl August Fürst von Hardenberg commissioned with the redesign of the building in 1817 to make it grander.
It was also Schinkel who recommended that the architectural beauty of two rooms along the building's central axis should be retained and remain untouched by the extensive remodelling of the rest of the castle. Other than that, Schinkel completely redesigned and rearranged the layout, and in particular the exterior, in the neoclassical style. Schinkel probably also had a major influence on the design of the interior; he may even have designed some furniture for it. However, most of the furniture and furnishings, which also included state chancellor von Hardenberg's library and his legendary art collection, fell victim to the general chaos at the end of the Second World War.
The main entrance, which has been graced by a triangular pediment with the inscription GRATIA REGIS ('Thanks to the King') since 1852, leads visitors from the courtyard directly into the above mentioned early neoclassical parts, which have remained intact since the original construction of the castle, and into a vestibule with elaborate stucco decorations. Consoles feature busts of Socrates, Homer, Cicero and Ganymede, for example, gifted by the Sparkasse Märkisch-Oderland savings bank to mark the official reopening of the castle. Following the main axis of the castle, next is the representative Garden Hall, whose three windows afford extensive views across the landscaped park. The walls are decorated with relief medallions, as well as some musical instruments and stucco panels. To the right of the Garden Hall is the 'Salon Bülow', which leads to the library. It originally contained around 16,000 volumes; six thousand of these now belong to the collection of the Central and Regional Library Berlin (ZLB). Like most of the other rooms, the 'Salon Bülow' was also named after a family related to state chancellor von Hardenberg's. In the 'Reventlow Room', which completes the eastern side of the building, two original panels by the artist Ernst Lössnitz (1866-1933) from Zeitz on permanent loan from the Reventlow family are juxtaposed with two modern paintings by the artist Sabine Funke from Karlsruhe. This is a prime example of the entire castle's artistic concept, which consistently seeks to establish a relationship between period elements and contemporary art. All of the rooms have been painted in colours that create a unified look and follow a colour concept that is a reinterpretation of the original neoclassical colours.
The building's largest room is located on the upper floor: the Hardenberg Hall with a huge conference table that seats up to 40 people. It is central to Neuhardenberg Castle's conferencing business. The hall is decorated with large-scale linocuts by the Munich artist Norbert Prangenberg. Further, more intimate rooms inside the castle are available for meetings and other events. The hotel's two exquisitely furnished suites are also located on the upper floor.