Hard choice but say 1960's to early '90s. So I could pop in to see Bob Dylan or see the Beastie Boys, Sonic Youth, Grandmaster Flash, Ramones, patti Smith, Run DMC, Jungle Brothers, Eric B and Rakim, The Stooges etc etc etc. Plus all the art going on. I'd even go and see John Coltrane and other jazz artists. Omg it'd be a feast.