To be privately owned
Kaiservilla

The Kaiservilla in Bad Ischl served as the summer residence for Emperor Franz Joseph I and Empress Elisabeth. This estate is the place where crucial decisions for European history were made.
History+
Originally a Biedermeier villa, the property changed hands in 1850 to Dr. Eduard Mastalier. Following the engagement of Emperor Franz Joseph I to Princess Elisabeth of Bavaria in 1853, Archduchess Sophie, the Emperor's mother, acquired the villa as a wedding gift. In the subsequent years, the building underwent reconstruction and expansion in the Neoclassical style under the direction of Antonio Legrenzi. The central section was extended towards the park, transforming the original rear into a grand entrance with columns and a tympanum. Two new side wings gave the structure the shape of an “E,” interpreted as a tribute to Empress Elisabeth. The entire ensemble, including the English park and the Marmorschlössl, was not completed until 1860, as no construction work was permitted during the imperial summer stays.
Source: Wikipedia · Licence: CC BY-SA 4.0 · Image: http://commons.wikimedia.org/wiki/File:Kaiservilla_vorderansicht.jpg
This description draws on the facts documented in the linked Wikipedia article; Wikipedia content is licensed under CC BY-SA 4.0. Wording and editing: Mobile History.
Location: 47.7150, 13.6209