Letná plain is a high flat terrain above the city. It is the traditional assembly point for invading and besieging armies and sports, and other cultural events. Under the Communists, Letná was used primarily for the annual May Day parades. Thousands trudged past the Sparta Prague stadium, where the Communist leaders would salute from their giant red podium. It used to boast the largest Stalin monument globally: a 30-metre-high granite sculpture portraying a procession of Czechs and Russians being led to Communism by the Pied Piper figure of Stalin. The monument was unveiled on May 1, 1955, but within a year, Khrushchev had denounced Stalin, and the monument was blown up in 1962. On the Stalin statue, overlooking the Vltava, stands a symbolic giant red metronome which was erected in 1991. The metronome is lit up at night and can be seen from the city centre. International artist Vratislav Novak designed the 75-foot-tall (23 m) Metronome. The area behind the metronome is also a popular skate spot where skateboarders from Europe and around the world congregate and film throughout the year.