Complex sentence: The tricana style's heyday was between the 1920s and the 1960s, when it had a strong impact both within Póvoa de Varzim and on outsiders visiting the city.
Split into simpler sentences: The tricana style's heyday was between the 1920s and the 1960s. In that time, it had a strong impact both within Póvoa de Varzim and on outsiders visiting the city.