Gedimino prospektas, running west from Cathedral Square, is the most important commercial street. On the southern side of Lukiskių aikštė, a square around 900m west of Cathedral Square, is Gedimino 40, Lithuania’s former KGB headquarters. The building also served as Gestapo headquarters during the German occupation and, more recently, the Soviets incarcerated political prisoners in the basement. It’s now the Genocide Museum (Genocido aukų muziejus), its torture cells and execution chamber making a grim impression. Well-labelled, detailed exhibits on Soviet occupation, deportation and Lithuanian partisan resistance are upstairs; the optional English-language audiotape commentary is worthwhile if you want a detailed prison tour.