Bern's city centre is largely medieval and has been recognised by UNESCO as a Cultural World Heritage Site. Perhaps its most famous sight is the Zytglogge (Bernese German for "Time Bell"), an elaborate medieval clock tower with moving puppets. Our hero Albert Einstein, whilst living at Kramgasse No. 49, developed the Special Theory of Relativity. His work on the General Theory also began in Bern. In June 1902, Einstein started work as a "technical expert third class" at the Patent Office in Bern. In 1908 he lectured at Bern University and in 1909 he resigned from the Patent Office in order to take up the post of associate professor of theoretical physics at Zurich University.