In the early years of the twentieth century the aging Franz Josef, kaiser to the great Austro-Hungarian Empire, visited the small village of Millstatt, on the northern shores of the Millstättersee in the Carinthian region of Austria. The village had grown up around a monastery whose origins dated back to the eleventh century. It now boasted an unusual twin towered church, a growing number of hotels and pensions, and a beautiful natural backdrop of forested alpine slopes around an unspoiled lake. The kaiser's visit brought the location to attention of the growing wealthy classes and very soon the area became a popular summer resort.

Among the visitors was a family from Schiebbs near Vienna. Ludwig Friedrich Musil Edler von Möllenbruck, son of a manufacturer of specialist paper, and his British-born wife were captivated by the beauty of the Millstättersee. They were to choose a steep, wooded slope above the lake as the location for a new summer residence. The building was to be patterned after a chateau in the French Loire valley and named Heroldeck after their youngest son, Herold.

Back in Vienna, they secured the services of an up-and-coming architect, Hans Prutscher. From a family of building restorers, Hans' most notable commission up to that time had been the refurbishment of Schloss Datschitz (Zámek Dacice) in Mähren. Now, von Möllenbruck was to give him his first opportunity to design and build. Just east of the village of Millstatt a plot was purchased that extended half a kilometer along the north shore of the lake. The plans then went ahead to build on a rocky outcrop around 70 meters above the water. Prutscher secured the services of the local baumeister, Anton Lerchbaumer, to oversee the project. Real work began in 1911, with much of the upper structure was to be in brick rather than the traditional Austrian materials of stone and wood. Over 100 workers were employed on the site, many of them Italians who came to the area seeking work at the mines in nearby Radenthein.
By 1912 the completed Schloss Heroldeck could be clearly seen from both ends of the lake. It was said that no expense had been spared in the construction. We have no record of the original interior, but it may be imagined that it would not have been a disappointment compared to the external appearance, and would have blended the popular late baroque style with the Louis XV and Napoleonic styles of the chateaux in France.

Hans Prutscher went on to design and build churches in the Vienna area; Baumeister Anton Lerchbaumer ran the Spittal based Ilbau AG, a successful construction company that was to grow into the international giant Strabag. Milstatt grew in popularity as a tourist in the that years followed the 1914-18 war, and the Schloss became an interesting feature in photographs and postcards of the period.

Before the Anschluss of 12 March 1938, the Möllenbruck family were pressured into selling the castle to the NSDAP for just 100,000 Reich marks. The property had been earmarked to become a "gauschule" or training school for NSDAP youth. An extensive building program was undertaken with the removal of the bell tower, front balcony, several windows and complete reorganisation of the interior. In 1938 a second building, now simply called “the Villa”, was completed on the property to the west of the main castle as an accommodation block.

Initially used as a facility for training young men and women, by late 1944 the premises were also being used to house children evacuated from the heavily bombed cities of Klagenfurt & Villach. Local testimony tells us that Else Bormann, half sister of the infamous Martin Bormann, was living at the Schloss up to 1945. At the end of hostilities, Schloss Heroldeck was used as a de-briefing centre for the Allies, and briefly housed some notable German officers including Field Marshal Albrecht von Kesselring.

By 1947 the property had been turned over to the newly formed Austrian government. Surviving family members were given the opportunity to re-purchase the castle, but were financially unable to do so. The building was put to use as a children's home under local administration. In 1950, with financial assistance from the Norwegian-European Assistance organization, the castle was developed into a convalescence and retreat centre for displaced and under privileged children. In the following years it would be visited by thousands of children from all over Europe. Schloss Heroldeck continued in its role as a children's home until it was placed up for sale in 1988. An Austrian couple, working with refugees from Yugoslavia, approached Calvary Chapel with the possibility of purchasing the facility for use as a refugee hostel.

The purchase went ahead in 1989, but as the barriers between East and West Europe began to come down, it was clear that different opportunities were opening up. Soon groups of volunteer workers arrived and began extensive renovations to prepare the castle for use as a retreat and Bible study centre. Initially Calvary Chapel invited Christian pastors and lay workers from the eastern-bloc countries to come and study in the peaceful surroundings. As time went on interest came from other Christian connections in Western Europe and the US.

Currently, the Schloss is just a private house, staffed by volunteers, but Christian individuals and groups come by invitation, for retreat, refuge, study, and just to enjoy the beautiful surroundings and fellowship that the Schloss provides.