Frederick's happiest days were spent as crowned prince in Rheinsberg. Miles away from his father's watchful eye in Berlin, he spent his time philosophizing about the world and playing music. Today, the castle on the lake in Rheinsberg still captures the spirit of Frederick's youth and curiosity. Frederick ascended to the throne in 1740. From that point on, he started Berlin's transformation from a small royal residence into a European metropolis. On Berlin's famous Unter den Linden boulevard, buildings like the state opera, Humboldt University and St. Hedwig's Cathedral still stand as testaments to the Prussian leader's vision. He also expanded Charlottenburg Palace, where the floors in the residency’s new wing pay tribute to the Rococo style of Frederick's time. In 1743, Frederick shifted his focus to Potsdam. His sketches and ideas gave life to Sanssouci Palace, the New Palace and many other royal structures that are major attractions in Potsdam today. The king's body has been buried in Sanssouci - his favorite residence - since 1991.