During the famine war in 1414, the castle was besieged by Polish knights and on July 6, it gained siege after eight days. In 1454 the castle was taken over by the Prussian Association of Prussia and in February 1455 he handed over to the Czech mercenary forces under Jan Kolda from Žampach, who repulsed the invasion of the Teutonic Knights on April 28 . In 1517 the outer bailey was extended and strengthened. In 1784, the outer bailey burned down. The most destruction was done by French soldiers stationed here intermittently in the years 1806–1812. The building, devastated by Napoleons, was rescued from the ruin by court counsel Ferdinand Tymoteusz Gregorovius, an effective originator of the reconstruction (1828-1830) of a medieval fortress intended for the seat of a court, private apartments and a prison. Gregorovius, however, reserved that the Nidz built a monument for him. The monument was built only over seventy years after the castle was rebuilt. The monument is located in the castle park. In 1945, the castle was not so lucky – bombed by the Russians, it burned down, losing ceilings and part of the walls. However, it was soon decided to rebuild it. In 1949, the building was removed from rubble, and three years later the first security works began. The complete restoration of the monument, including the conservation of the preserved paintings in the chapel and refectory, began in 1961 and was completed in 1965, after which it was solemnly put to use by local cultural and social institutions.
Currently, the castle serves as a city center for business, culture and entertainment. It houses: the Museum of the Nidzica Region with an ethnographic and historical exhibition, the Nidzica Cultural Center, the Knights’ Brotherhood of the Nidzica Commander’s, Hieronim Surpski’s Author’s Gallery, a sculpture studio and a city library. A hotel and restaurant also operate here. Admission to the outer ward and the courtyard of the high castle is free, to the museum is paid. The complex is surrounded by a dense 19th-century park.
The stronghold was built of brick on a high stone foundation. In the attic, in the thickness of the walls, the castle is surrounded by defensive cloisters both from the outside and from the courtyard. The façade on the west side is covered with dark brick. The external facade is also decorated with large ogival Gothic windows. In one of the rooms, closed with an apse, Gothic frescoes from the turn of the 14th and 15th centuries are still visible. The middle part played the role of a refectory with a readable, though damaged wall painting of Saint Veronica in adoration of angels. The refectory was adjacent to the head office of the commune head. Granaries and defense galleries were located on the last floor of the western part of the castle. Towers covered with tent roofs were decorated with alcoves and flat decorations. There was a prison in the cellars of the towers. Above the gate was a castle chapel occupying two floors. In this part of the castle chambers for the guests of the order were located, here also the head of the village and chaplain lived. Knights, squires and armed service were quartered in the side wings of the building. In the castle courtyard there was once a well supplying the crew with water. On the eastern side from the entrance was the outer bailey, rebuilt in 1517. In the southeast corner of the outer bailey a round tower rose. The spiral staircase of the tower led to the living quarters of the east wing. In 1583, another one flanked with two small cylindrical towers was added to the existing ward (this ward burned down in 1784). Old oak grows in its place today. At the end of the 15th century, the castle was surrounded by an external wall armed with two round bastions.