Some of the windows in the corner rooms of the first floor were walled in so as to create more display space. Four of the five doorways between the Grand Gallery and the Hercules Hall, and all window openings above them, were closed in order to create enough space to hang Rubens’ Decius Mus cycle in the Grand Gallery. This wall had previously been decorated like the outer wall of the hall, with the windows illuminating Pozzo’s ceiling fresco from the second side as well.

Changes were also made to the second floor, in particular the staircases. Some of Bellucci’s ceiling paintings, which had been removed from Bankgasse in 1819, were put on immediate display there as part of the museum. Rottmayr’s frescos in the stairways had suffered partial water damage and disappeared for nearly two centuries under two giant ceiling paintings, each with four satellites by Bellucci. The areas left uncovered were plastered over.

The walls of the gallery rooms were painted in shades of green and blue, following a relatively uniform concept. Both a 1902 watercolour by Raimund von Stillfried and the earliest photographs confirm this. Objects were displayed in an unbelievable density, as was to be expected of a princely Kunstkammer. This would be compatible neither with today’s concept of a museum nor with current standards of safety or aesthetics.

Periodic changes were made during the palace’s use as a museum. After the Hercules Hall had been decorated in a classicistic manner, the early 20th century saw these changes to the original baroque fabric reversed. Neo-baroque décor such as fireplaces and elaborate stuccowork on the end walls of the Hercules Hall were added. The five paintings by Franceschini hanging on the long wall were also added during these adaptations.

This period also saw plans to enhance the serenely classicist early nineteenth-century stucco ceilings of the stairways with magnificent baroque decor, in keeping with contemporary tastes. However, these plans were never brought to fruition.

Another project never to be realised was the decoration of the bare wall surfaces with pieces from the collection of ancient artefacts which still existed at that time.

Further major alterations were made necessary by the transfer of the library from the classicist Majoratshaus designed by Hardtmuth in Herrengasse, after this building had been evacuated, sold and finally surrendered for demolition in 1913. This library was housed in the Gentlemen’s Apartment on the ground floor of the Garden Palace.

The library is the sole remaining element of one of the main works of early Austrian classicism and, together with the frescos by Rottmayr, forms a unique ensemble which has evolved over the centuries.

The archives were moved into the Ladies’ Apartment following installation of the necessary steel shelving units.