The first major constructions were carried out in the 17th century by István Kálnoky III (judge of the Court of Appeal), who in 1648 noted in his diary the start of the building process on the "Miklósvári stone house". A rectangular, two-storey castle was built then in Late-Renaissance style. The eastern, southern and and northern walls were reinforced by two bigger and two smaller polygon-shaped bastions. In the last decades of the 17th century Sámuel Kálnoky I (son of István Kálnoky) further expanded the building. The Great Hall was ornamented then with stucco motifs, a very unique technique of the Late-Renaissance style in Transylvania, which is quite similar to the Jesuit church in Nagyszombat. The Catholic Sámuel Kálnoky supported the settlements of the Jesuits in Transylvania, therefore it is possible that he invited an expert from Western Hungary to put into effect the decorations of the castle. Due to his order a small, closed balcony was built on the central axis of the south façade, which resembles the balcony in Bethlenszentmiklós, and it lies on two carved stone consoles and on a stone cannon tube. The initials of the builder (SK) are carved on the balcony.

Dénes Kálnoky I (1814-1888) was the last proprietor from the Kálnoky family. As he died without descendants his sister’s son Ferenc Seethal inherited the castle. The current style of the castle and the form of the main façade are related to his building activities. The constructions between 1902-1905 were led by Péter Kreigher (a mason from Sfântu Gheorghe) based on the plans of Győző Gyárfás (engineer). The castle was surrounded by a huge English Garden (created in the 19th century) from which only a few rare tree types can be seen today. In 1939 after the death of Ferenc Seethal the castle was sold to Eugen Savu (Minister of Finance during the Goga government) but he lost it during the nationalization period. In 1997 carved stone pillars with unique floral ornamentation, which held the arcades, were discovered in the walls of the building.

During the 20th century different changes were carried out because after the nationalization the aim was to transform the building into a community house, therefore they have built a stage in one of the rooms. At the beginning of the 20th century the castle was rebuilt in a Classicist style but the Late- Renaissance character of it was still visible. By the way of its construction and decoration preserves the memory of Háromszék, mirroring the pretentions and aspirations of a local nobleman who led the constructions at the end of the 17th century. At the end of the 1990’s the descendants inherited the building, which under the Kálnoky family’s care was renovated. The local government of Baraolt signed a contract for 49 years with Tibor Kálnoky, who moved back home from Germany, because he intended to use the mansion in the field of tourism.

The former two-story Renaissance styled mansion with a rectangular layout was reinforced on the east, south and north sides with polygon shaped bastions. The wall structures of the corner towers, the loopholes, the extremely thick stone walls of the basement together with the moat served the protection of the castle. Due to the Renaissance stone carvings the building is particularly valuable. The most important features are the Renaissance windows of the south-east tower, decorated with tympanum and notch, and the door/window frames carved from red andesite. On the central axis of the north-east-facing façade there is a Classicist balcony. The stairs which lead up to this balcony are decorated with small, spindle-shaped pillars. The triangular pinnacle of the porch was once decorated with the crest of the Kálnoky family. Today only a few traces of the relievo can be seen. Both sides of the façade are decorated with avant-corps, which is similar to the ornamentation of the porch, which comprise semi-circular shaped staircases. On the side of the main façade, where today the columned porch stands, up until the beginning of the 20th century the pair of a small balcony could be seen. The decoration and design of the interiors has changed a lot over the centuries. The halls were covered with flat ceiling and barrel-vault ceiling. The decoration consisted of stone frames and stucco, which had been recently discovered. On the northwest part the arches and pillars of the former open-porch can be seen together with the recently restored, ornately-carved door frame, which leads from the porch into the building. Other decorative elements are the lion heads holding rings in their mouth and the scroll-works framing the cartouche on which the motto of the Kálnoky family is inscribed: NON EST MORTALE QUOD OPTO. The doorways are decorated with frames made of red andesite, which have a Late Renaissance style. During the inspection of the walls, in the great hall of the castle, also known as “the palace“, traces of stucco were discovered. In the 18th century the open porches were closed with walls and the painted, incised ornaments of the facades were finished. In the 19th century a separate premise for the toilets was built between the right side of the southwest tower and the small porch on the southeast side. In 1974, after the regime change, the building was restored by the government.