What route did the western allies use to approach the soft underbelly of europe?

Allied forces invasion (salerno d say paln) of Italy happened on 3rd september 1943, during wrold war II. western allies consisted of france, poland and UK. Italy is referred as the "under belly of europe". This invasion was named as "Operation Avalanche". They entered through Salerno from west coast. another two supporting operations namely "Operation Baytown" and "Operation Slapstick" happened in Calabria and Taranto respectively. Finally Italy surrendered to Allied nations