With a population of 193,000, Trondheim is not a big city on a European scale. However, it is the third largest in Norway. Trondheim has a number of sights that each year are among the most visited in Trøndelag. The Nidarosdomen cathedral is an impressive sight. The cathedral is the national sanctuary of Norway, built over the grave of St. Olav. Work began in 1070, but the oldest parts still in existence date from the middle of the 12th century.