Krzyżtopór is a castle located in the village of Ujazd, Iwaniska commune, Opatów County, Świętokrzyskie Voivodeship, in southern Poland. It was originally built by a Polish nobleman and Voivode of Sandomierz, Krzysztof Ossoliński (1587–1645). The castle was partially destroyed during the Swedish invasion known as The Deluge in 1655, and then reduced to ruins during the war of the Bar Confederation by the Russians in 1770.
Built inside massive stone walls with bastions at the five corners, this mannerist palace embodied the structure of the calendar. It had four towers symbolizing the four seasons and 12 big halls, one for each month. Exactly 52 rooms were built, one for each week in the year, and 356 windows. The building occupied an area of 3.2 acres, its walls were 600-meter-long and its cubature amounted to 70 thousand cubic meters. Marble and mirrors were used in the interiors of the underground stables, while the ball room had an aquarium in place of the ceiling. The water supply installations used water from the local spring, and rooms were heated with warm air coming to them through special air passages.