Atop Toomemägi are the ruins of a Gothic cathedral, originally built by German knights in the 13th century. It was substantially rebuilt in the 15th century, despoiled during the Reformation in 1525, used as a barn, and partly rebuilt between 1804 and 1809 to house the university library, which is now a museum. Inside there are a range of interesting exhibits chronicling student life.
Start by taking the historic 1920s lift to the top and working your way down. Morgenstern Hall retains the appearance of the historic library and is lined with statues of the Ancient Greek muses. Kids will love the Cabinet of the Crazy Scientist, where they take part in some hand's on science themselves. Other highlights include the beautiful White Hall and the Treasury, which houses eclectic items such as the death mask of Russian poet Aleksandr Pushkin, a 1504 Dürer print, a human hand once used for anatomy lessons and a set of elaborate cheat-sheet scrolls extracted from students in the 1980s.
From May to September the museum ticket also includes entrance to the viewing platform on top of the cathedral tower.