What peninsula creates the heel of an Italian boot?

The Apennine Peninsula extends 1,000 km (620 mi) from the Po Valley in the north to the central Mediterranean Sea in the south. The peninsula's shape gives it the nickname lo Stivale (the Boot). Three smaller peninsulas contribute to this characteristic shape, namely Calabria (the "toe"), Salento (the "heel") and Gargano (the "spur").