Where did Italy surrender?

There was no real place of surrender. The Italian Government ousted Mussolini in July 1943 and tried to negotiate a peace with the Allies. After the Allied army landed at the "toe" of Italy the first week of September and they detected a naval invasion force headed towards Salerno, they agreed to surrender on 8 September 1943.
But it was too late. The Germans began occupying their country and fighting on their land. The war in Italy continued until May 2, 1945 when the GERMAN leaders signed a surrender. I think they met secretly in Switzerland to agree on a surrender. The formal signing was at Caseratta, the Headquarters of the Allies in Italy.