The castle was built between 1651 and 1654 by the Zittau master builder Valentin for Mayor Christian von Hartig. It has a rectangular floor plan, and the castle entrance is flanked by two octagonal towers with Italianate cupolas. The smaller right tower was added as a stair tower in 1853. The vestibule is also an addition from 1892. On the older, left tower, a plaque embedded in the wall bears the following inscription:
"For the pleasant leisure,
for honorable pursuits, and for the spirit of the place,
because of the charm of the location, this part has been dedicated by Christian von Hartig in Hörnitz, Knight of the Order of St. Mark."
The lower floor of the old tower is covered by a cross vault. Here, Hartig's son, Jakob, conducted alchemical experiments with Ehrenfried Walther von Tschirnhaus, inventor of the burning mirror and fundamental researcher for Meissen porcelain. The laboratory caught fire. Jacob fled, and the terrified villagers secured the expulsion of the magician Tschirnhaus. It is certain that important discussions about the development of Meissen porcelain took place in Hörnitz. Tschirnhaus then supervised Böttger's experiments. Christian von Hartig was the first in Zittau and the surrounding area to operate a greenhouse, a hothouse, and an orangery, for which he introduced rare flowers. Althörnitz remained in the possession of the von Hartig family until 1771. They were succeeded by Karl August von Kyaw, who sold it to Johann Gottfried Kämmel of Waltersdorf in 1781. In 1826, it belonged to Ernst Wilhelm Friedrich Just, from 1840 to Moritz von Beschwitz of Großschweidnitz, and from 1871 to Mr. Heisen of Annaberg, who immediately thereafter built a steam distillery for potatoes and one of the largest cowsheds.
Afterwards, in 1881, the Saxon chamberlain Hans Rudolf von Sandersleben acquired the manor and the associated land. Neuhörnitz and Althörnitz were united on July 1, 1912. After the Second World War, the von Sandersleben family was expropriated, and the property was subsequently inhabited by resettlers. From 1948 to 1991, vacationers from the Federation of Trade Unions of the GDR (FDGB) were cared for here under simple conditions. Despite significant support from the municipality of Bertsdorf-Hörnitz, the buildings subsequently fell into disrepair.