The castle in Bobrowniki may have been built around the middle of the 14th century from the foundation of Władysław Garbaty, the Duke of Dobrzyń, although archaeological studies postpone the date of its construction to the end of the 14th century. In this case, its builder could be Prince Vladislaus II of Opole, who owned the Dobrzyń land as a feud in 1379-1392. Finishing works could also be carried out by the Teutonic Knights who occupied the local lands in the period 1392-1404, although the preserved documents only provide information about their minor works being carried out at that time.
During the wars of the second half of the fourteenth and the beginning of the fifteenth century, the castle repeatedly passed from the hands to hands. In 1391 it withstood the siege of the Polish army, then returned to the Polish king, but in 1409 it was again captured by the Teutonic Knights. Finally, after 1411, it returned to Poland and on the initiative of king Władysław Jagiełło was considerably expanded. When the Second Peace of Toruń in 1466 ended Polish-Teutonic war, the castle lost its military significance and became the seat of the staroste. In the seventeenth century it was ravaged by the Swedes, although, as the graphics from 1627 show, it was previously partly ruined. Eventually, it was pulled down in the 19th century.
The castle was situated on an artificial, not very high embankment, on the right bank of the Vistula, the bed of which protected it from the west and partially south. In the close vicinity, the small river Gryzka also had its outlet, flowing on the eastern side of the castle and flowing into the Vistula in the north.
The oldest core of the castle was built on a square plan with a sides of about 46.5 meters. It consisted of simple curtains of defensive walls, the main house forming the south-west part of the castle, a cylindrical tower with a four-sided base measuring 10.7 x 11.2 meters and a low gatehouse. The latter was located outside the north-west curtain, on a plan similar to a square with dimensions of 10.5 x 11.5 meters. The interior of its ground floor housed a vaulted gate passage about 3 meters wide and a small, also vaulted, room of the guards. The perimeter walls, with an impressive thickness of more than 3.5 meters, were reinforced from the outside with buttresses, both in the corner and in the curtains line. As the gatehouse in the side walls had posterns, external fortifications in the form of a timber palisade could function before the erection of the second brick perimeter.
The main residential house was 15 x 46 meters, it was a single-track building with a basement and two above-ground storeys covered with a gable roof. At the basement level, the interior was divided into three rooms and this division was probably repeated also on the upper floors. The second, smaller building was situated between the main tower and the house, along the south-eastern curtain of the wall. In addition, wooden auxiliary buildings of an economic function could also function at the north-eastern section of the wall.
In the 15th century, the castle was expanded with a circumference of external brick walls, located approximately 12.5 meters from the main perimeter and also reinforced with buttresses. What is unusual, they had a considerable thickness, similar to the inner ring of fortifications. In the fifteenth century, the gate was also extended by a foregate, and small towers were built in the corners of the second perimeter, perhaps adapted to fire defense. The outer defense zone was an irrigated moat surrounding the castle from the land side. Later reconstructions, perhaps even late medieval, were associated with the paving of the courtyard and the construction of earth ramparts that protected the castle from the north and east.
Currently, only the elements of the defensive walls, mainly the northern and southern part, as well as the relics of the tower, which in the highest place has been preserved to a height of 11.8 meters, are a trace of the former splendor of the building. Picturesque ruin is open to visitors.
Leksykon zamków w Polsce, red. L.Kajzer, Warszawa 2003.
Pietrzak J., Zamki i dwory obronne w dobrach państwowych prowincji wielkopolskiej, Łódź 2003.