Letná plain is a high flat terrain above the city. Letná plain has long been the traditional assembly point for invading and besieging armies, as well as sports and other cultural events. Under the Communists, it was used primarily for the annual May Day parades, during which 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 in the world: 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 site of 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. The 75-foot-tall (23 m) Metronome was designed by international artist Vratislav Novak. The area behind the metronome is also a popular skatespot where skateboarders from Europe and around the world congregate and film throughout the year.