The site on the Portz Insel island is thought to have been founded by Prince and Cardinal Franz von Dietrichstein (1570–1636), who began the extensive reconstruction of medieval Mikulov and also had extensive alterations performed to the landscape around Mikulov, including the island site in the Portz Pond. We know from the urbarium or land register of the Mikulov Estate of 1629 that part of this site was also the summerhouse and its ornamental garden, as well as farm buildings and large cellars in the form of a system of galleries. Although the urbarium does not mention the bridge itself, it can be assumed that access to the island must have been assured in order to supply building materials for the summerhouse. The rectangular two-storey summerhouse building was built as a “Villa suburbana”. A large hall and a smaller backroom that opened out onto the terrace situated on both gable fronts were located on the upper floor. Access to the upper floor was provided by an exterior double stone staircase with a balustrade. A kitchen and other auxiliary premises were situated on the ground floor which was directly connected with a labyrinth of underground galleries that led to the nearby farm building that contained the apartment of the site manager. The summerhouse is located on an elevated brick terrace around 80 x 70 metres in size with bastions jutting out at the corners. This design was evidently intended to evoke a fortified summer house based on Italian designs for fortified architecture known as palazzo in fortezza. It is possible that a planner strongly influenced by Italian architecture played a part in its design.
The draining of the original Portz Pond in the middle of the nineteenth century and the subsequent division of the island into two halves by a new railway line built in 1872 had an enormous impact on the use of the summerhouse and the adjoining game park. The park on the island was, nevertheless, maintained until the beginning of World War II, as is confirmed by a record from 1937 testifying to a visit to the summerhouse by the Duke and Duchess of Windsor. Only the northern part of the original pond was restored after World War II and it has been known as the New Pond since that time. Unfortunately, the fact that the summerhouse and its surroundings found themselves in the immediate vicinity of the state border with Austria, i.e. in the heavily guarded border zone, had a considerably negative impact on the rest of the island site. All of the buildings and the park fell into a state of complete disrepair and became overgrown with vegetation as a result of the fact that they were completely inaccessible throughout the second half of the twentieth century.
A new chapter in the history of the site didn’t begin to be written until after the events of 1989. It was declared a cultural heritage site by the Ministry of Culture on 3 August 1995. The summerhouse itself became the property of the town of Mikulov, which sold it to a private owner in 2002 who began the overall restoration of the site in 2003, the first stage of which involved the clearance of all the overgrown vegetation growing in the ruins of the summerhouse and the entire area surrounding the elevated terrace. The new owner also assured the static safety of the building, gave it a new roof and a new exterior double stairway, and began repair work on the façade of the summerhouse.
Another new owner continued the gradual total renovation of the site in 2013, completing the renovation of the exterior cladding of the summerhouse and the installation of the balustrade handrail on the access staircase and, perhaps most importantly, the extremely demanding overall restoration of the interiors on both the ground floor and first floor, along with a new residential loft conversion. This new owner also performed the static assurance of the supporting walls of the elevated terrace from three sides, including the corner bastions, and the overall renovation of the original extensive labyrinth of underground galleries, including their connection with the infilled part of the summerhouse. The ruins of the farms buildings were also cleared of overgrown vegetation and, last but not least, new vineyards were planted on part of the cleared areas of the original historical park immediately surrounding the summerhouse. This is associated with the business activities of the new owners who run a winery – their wines, which are stored in part in the original underground spaces, can be tasted at the summerhouse, and refreshments are also offered by a bistro kiosk established in part of a former farm building.
The owners plan, however, to complete the static assurance of the final side of the bastion as soon as possible, after which they want to renew the ornamental garden on the elevated terrace. Last but not least, they plan to restore the summerhouse’s farm building.