Vaduz Castle is the palace and official residence of the Prince of Liechtenstein; the castle gave its name to the capital town of Vaduz, which it overlooks from an adjacent hilltop. The first owners and presumably the builders were the Counts of Werdenberg-Sargans in the 12th century.
A lovely card sent from which must have been a great PC meeting in such settings, thank you Diana! :))
(I have seen the castle on an early morning drive-by, it was closed to the public :()