After he became ruler in 1740, Frederick the Great personally planned the buildings surrounding this square. The area received the nickname Forum Fridericianum, or Frederick's Forum. A music lover, Frederick had as his first priority the Staatsoper Unter den Linden. Berlin's lavish opera house was completed in 1743 by the same architect who built Sanssouci in Potsdam, Georg Wenzeslaus von Knobelsdorff. Daniel Barenboim is maestro of the house. Unter den Linden 7, Mitte. 030/2035-4555. www.staatsoper-berlin.de. Box office weekdays 11-8, weekends 2-8; last hr for tickets to that night's performance only; reservations by phone Mon.-Sat. 10-8, Sun. 2-8. Französische Str. (U-bahn)

The green patina dome belongs to St. Hedwigskathedrale. Begun in 1747, it was modeled after the Pantheon in Rome and was the first Catholic church built in resolutely Protestant Berlin since the 16th-century Reformation. It was Frederick the Great's effort to appease Prussia's Catholic population after his invasion of Catholic Silesia (then Poland). A treasury lies inside. Bebelpl., Mitte. 030/203-4810. www.hedwigs-kathedrale.de. Free. Weekdays 10-5, Sun. 1-5. Tours (EUR 1.50) available in English, call ahead. Französische Str. (U-bahn)

Running the length of the west side of Bebelplatz, the former royal library is now part of Humboldt-Universität (Unter den Linden 6, Mitte), whose main campus is across the street on Unter den Linden. The university building was built in 1766 as a palace for Prince Heinrich, the brother of Frederick the Great. With its founding in 1810, the university moved in. The fairy-tale-collecting Grimm brothers studied here, as did political philosophers Karl Marx and Friedrich Engels. Albert Einstein taught physics from 1914 to 1932, when he left Berlin for the United States. On May 10, 1933, Joseph Goebbels, the Nazi minister for propaganda and "public enlightenment," organized one of the nationwide book-burnings on Bebelplatz. The books, thrown on a pyre by Nazi officials and students, included works by Jews, pacifists, and Communists. In the center of Bebelplatz, a modern and subtle memorial marks where 20,000 books went up in flames.