The Renaissance Water Castle of Blatná — A water stronghold was established here in the 13th century under Vyšemír (documented as a witness on a charter of King Wenceslas I from 1235) and the squires of Blatná resided here. The castle took its name from its location on a rocky outcrop rising above marshes. At the end of the 13th century it was acquired by their relative Bavor of Strakonice. After the last member of this family, Břenek, documented as late as 1403, Blatná was acquired by a distant relative, Jan of Rožmitál — also known as Jan of Blatná — first documented in 1408 and then again in 1424. He had the Romanesque seat of the Bavors completely demolished and in its place had a Gothic castle built. Of the Romanesque castle only a part of the ground floor of the chapel was preserved, discovered in 1926 during the investigation of a Romantic ruin from the early 19th century.

The lords of Rožmitál, from whose family also came Johanka, wife of King George of Poděbrady, deepened the marshes into a pond, in the process burying the last remains of the original building under an embankment up to 3 metres high; the enlarged area was bounded by a wall, in front of which there was the necessary water moat and rampart. Traces of this fortification have been partly preserved to this day. Access to the castle was, as before, from the east via a drawbridge, at the end of which stands a tall prismatic tower. Above the portal are set the stone coats of arms of Jan of Rožmitál and his wife Eliška of Kravař. Adjoining the tower on the left is the Gothic palace with a chapel on the first floor. At the same time a second palace was built on the site of the former Romanesque castle. Since water castles, and castle new-builds from the 15th century in general, are rare in the Czech lands, we can observe at Blatná castle some entirely new features — above all in the arrangement of the fortifications, which have been partly preserved to this day.

Jaroslav Lev of Rožmitál (1446–1485), Grand Justiciar of the Land and Grand Hofmaster, also resided here and continued the building work. He led the famous embassy (1465–1467) of King George of Poděbrady (whose wife was Jaroslav's sister) to European monarchs. The journey of Jaroslav Lev of Rožmitál — leading a group of 40 Bohemian lords and knights — led through Plzeň to Nuremberg and further to Brussels, England, France, Spain and Portugal, to the end of the known world. The embassy returned home via Italy and Austria. King George was in a difficult position. Six years after his election as king, Pope Pius II revoked the Basel Compacts — the agreement between the Czech Hussites and the Council of Basel. The revocation of the Compacts renewed the effort to isolate Hussite Bohemia and root out Wycliffites, Hussites and other heretics. George of Poděbrady attempted to counter this effort through extensive foreign policy activity. The pinnacle of his diplomatic activity was the embassy to Christian monarchs — apparently the first detailed blueprint for an international organisation conceived on the principles of co-operation between mutually equal sovereign states and the fulfilment of assumed obligations, principles that today form the foundation of the United Nations. The diary of Václav Šašek of Bířkov from this long journey became welcome material for Alois Jirásek's book From Bohemia to the End of the World.

From the time of Jaroslav Lev of Rožmitál undoubtedly date the uncovered and restored late Gothic frescoes in the so-called Knight's Hall of the Bavor Palace (figures of kings, a tournament scene, court scenes, depictions of Rožmitál and Blatná, etc.) and in the so-called Green Chamber in the castle tower (figurative scenes in rich ornamental decoration, coats of arms of leading noble families in Bohemia — the Švamberks, Rýzmberks, Rožmberks, Gutnštejns, Zajíc of Házmburk, Berk of Dubá, etc.).

The era of Rožmitál lordship represented the period of greatest flourishing for Blatná. For the architectural development of Gothic Blatná did not end with the building activity of Jaroslav Lev of Rožmitál. His son Zdeněk Lev of Rožmitál (c. 1470–1535) ranked among the leading officials of the provincial government in Bohemia (Grand Burgrave 1507–1523 and again 1525–1528), politician and adviser to Kings Vladislaus II and Louis. His first building undertaking was the extension of the castle chapel in the Bavor Palace with a three-sided chancel. After the walls were painted with biblical scenes, the Chapel of the Virgin Mary was consecrated in 1515. Far more important was Zdeněk's decision to build a new wing at the Bavor part of the castle, to the design of the royal architect Benedikt Ried (Rejt), which combined Gothic and Renaissance elements. Construction was begun after 1528. Both facades are penetrated through two floors by pairs of triangular bay windows. The castle courtyard on the western side was apparently enclosed by a ground-floor loggia. The palace has a wholly original layout.

The costs of building works, the dignified representation befitting his official and social position, expenditure on official and diplomatic journeys, and loans provided to King Vladislaus II plunged Zdeněk Lev into debt. The income from the two main estates, Rožmitál and Blatná, and the sluggish repayments from the royal treasury were insufficient to cover all expenditure. And so after Zdeněk's death in 1535, his son Adam of Rožmitál had to sell off the entire inheritance and move to Moravia. Blatná was acquired in 1541 by one of Zdeněk's creditors, Adam of Šternberk, who in 1555 sold it to the sisters Kateřina and Anna Řepická of Sudoměř. In 1560 Kateřina ceded Blatná to her husband Zdeněk of Šternberk. By this time the gradual transformation of the castle into a Renaissance château had begun.

After Šternberk's death (1575), Blatná was acquired in 1579 by the Polish nobleman Count Jan of Rozdražov (died 1585). His son Václav built beside the castle tower, on a hitherto unbuilt site at the northern wall, a two-storey Renaissance palace. The gap between this new wing and the old Gothic building further to the west was filled by a low building with a kitchen and servant quarters. This essentially concluded the architectural development of the Blatná château.

Blatná remained in the possession of the lords of Rozdražov until 1691, when the family died out with Jan's grandson František Ignác. The Blatná estate was inherited by Count Jan František Krakovský of Kolovrat, whose mother came from the Rozdražov family, but in 1695 he sold Blatná to Countess Arnoštka Serényi. After the fire of 1763, which most severely damaged the Rozdražov wing, this building was given a baroque conversion during the following four years. Under the Serényi family, an Empire-style pavilion with a projecting double staircase was built in the adjacent game reserve.

The last family to own Blatná were the Hildprandts of Ottenhausen. In 1798 Václav Karel Hildprandt of Ottenhausen purchased the Blatná estate from Amand Serényi. His son František Hildprandt, whose private tutor in philosophy and natural sciences in 1810–1813 was Jan Evangelista Purkyně (who founded a library here), had in 1850–1856 a free view from the courtyard into the English park opened up by demolishing the Romanesque chapel and loggia. The entrance space behind the tower was newly adapted, as was the old Bavor Palace; in the adjacent Ried building the interconnection of rooms was altered. In 1809 the wooden drawbridge was removed and replaced by a stone bridge. Through the remodelling of the château in the English Gothic style in 1850–1856 to the design of architect Bernhard Gruber, Blatná acquired its present appearance. At the same time the adjacent game reserve was transformed into an English landscape park (42 ha).

The château has an approximately rectangular ground plan. Entry to the château is via a bridge (formerly a drawbridge). The massive entrance tower is a remnant of the original stronghold. The courtyard is open at its rear end towards the park. On the left side of the courtyard is the Ried wing from the 16th century; opposite stands a newer building from the 17th century.

In 1945 the château passed into state ownership. In the 1980s it underwent a general overhaul. In 1991 the château was restituted to the Hildprandts. The interior exhibition was changed; it is now largely devoted to members of the Hildprandt family. The valuable Ried wing from the 16th century is now in poor condition. It is to be hoped that reconstruction work will begin soon.

The treasure supposedly hidden at the former castle by the Templars, however, would be searched for in vain. It is said that two centuries ago a clever clerk found it and carried it off, guided by instructions on an old painting.