Discover the delightful old centre of the capital, Luxembourg City. See the grand squares and winding, cobblestone streets. Visit the underground tunnels, known as casemates, and hop on the special open-air tourist train through the Pétrusse Valley. See the changing of the guard at the Palais Grand Ducal, the Grand Duke’s official residence, which can also be toured in July and August. Other attractions in the city include the Place Guillaume II (also called Knuedler), its twice-weekly market (Wednesday and Saturday); and the 17th-century Notre Dame Cathedral.