Amongst the most visited sights is the Masurian Lake District, which contains more than 2,000 lakes, including the largest lakes of Poland, Śniardwy and Mamry. Other recognizable landmarks are the Warmian castles (Lidzbark Warmiński Castle, Pieniężno Castle, Olsztyn Castle) and the Cathedral Hill in Frombork, where Polish astronomer Nicolaus Copernicus lived and worked. The Lidzbark Warmiński Castle was later the residence of Ignacy Krasicki, nicknamed "the Prince of Polish Poets". The Grunwald battlefield in Masuria is site of the annual reenactment of one of the largest battles of Medieval Europe. Święta Lipka in Masuria and Gietrzwałd in Warmia are popular pilgrimage sites.