Built in the beginning of the 17th century, the Royal Castle of Warsaw - or Zamek Krolewski - marks the entrance to Old Town, and was the official seat of the Polish monarchy up until the beginning of the 19th century, and also housed the Polish Parliament throughout history. Although, like most of Old Town, the castle was destroyed during World War II, it underwent major reconstruction between 1971 and 1984, and is now fully open to the public.
The beautiful brick facade of the castle is bookended by the bulbous spires so common to Polish architecture, and the castle square alone is worth visiting. In addition to the classic Polish architecture, Italian influences are strong, as the palace was designed by an Italian architect. As such, the building is exquisite, and should be on every Warsaw visitor's agenda.
Containing an incredible collection of artwork and art objects, the interior of the castle is a beautiful also houses part of the National Museum, as well as functioning as a frequent meeting place for the Ministry of Culture. The different rooms of the palace are decorated with amazing attention and fealty to the original state, before the war. Be sure to pick out the two Rembrandts that were donated in 1994 by the Countess Karolina Lanckoronska.