Zurich's most imposing cathedral, the Grossmünster, is said to have been commissioned by Charlemagne to be built on top of the graves of Felix and Regula, the city's patron saints. A city landmark, the twin towers of the Romanesque-style Protestant Church rise up over the banks of the Limmat, and an intricate iron door under beautifully carved gothic arches marks the entrance. Inside is a Roman crypt and more modern stained glass windows by Swiss artist Augusto Giacometti, nephew of the his more famous and abstract uncle, Alberto Giacommeti.