The Neuschwanstein castle in Germany's Bavaria, perhaps best known for inspiring Walt Disney's fairytale castles, has been named a World Heritage site, the UN cultural agency announced on Saturday.
Three other royal residences, also constructed in the late 19th Century under the famously arts-obsessed King Ludwig II of Bavaria, were also added to the coveted list: Herrenchiemsee, Linderhof and Schachen.
Neuschwanstein, perched on a rocky, 200m-high Alpine crag, is Germany's most visited castle, with almost 1.5 million people flocking there every year.
"A fairytale comes true for our fairytale castles: We are #WorldHeritage!" Bavaria's governor, Markus Soeder, wrote on X after the announcement.
Neuschwanstein combines an idealised medieval exterior with architectural techniques considered cutting-edge at the time.
Its main rooms are adorned with paintings of German and Nordic legends, the same stories that inspired composer Richard Wagner, for whom Ludwig was a generous patron.
Peter Seibert of the Bavarian Castles Administration (BSV) told AFP that the UNESCO listing "is a very great responsibility, but also recognition... for the work we have done so far in preservation".
Philippe, a 52-year-old visitor from Canada, was surprised that the castle was not already a World Heritage Site.
"We're lucky to still be able to experience this," he said, calling the listing "a very good idea".
Herrenchiemsee meanwhile evokes a Versailles in miniature on a lake between Munich and Salzburg, an homage to absolute monarch Louis XIV of France, whom Ludwig admired.
Indeed Ludwig nicknamed Herrencheimsee "Meicost-Ettal", an anagram of Louis XIV's alleged aphorism "L'Etat, c'est moit" ("I am the state").
The third site in the UNESCO listing is the small castle of Linderhof, completed in 1878, the only one to have been finished in Ludwig's lifetime.
It mixes elements of French Baroque architecture from the reign of Louis XIV with touches of the Rococo style developed in southern Germany.
Its park boasts an artificial cave inspired by Wagner's opera Tannhaeuser, 90 metres long and up to 14 metres high, which houses a grotto of Venus and was designed as a personal retreat for Ludwig.
The electric lighting system used in the cave was state of the art at the time, with glass discs used to illuminate the grotto in different colours.
The last of the four sites on the list is Schachen, a royal house in the style of a large Swiss chalet, where Ludwig liked to celebrate the saint's day of his namesake St Louis on August 25.
It is located at 1,800 metres above sea level, not far from Neuschwanstein.
The four castles have become "part of Bavarian identity" says Seibert, "iconic and perfectly embedded in a beautiful landscape".
Ironically, while Ludwig's architectural legacy is today a source of pride in Bavaria -- not to mention tourist revenue -- they were part of the reason for his own downfall.
The ruinous construction costs of the lavish residences led the Bavarian government to depose him, declaring him insane.
Interned in Berg Palace, he died shortly afterwards in mysterious circumstances at Lake Starnberg.
