Short answers, pulled from the story.
The Italian Peninsula is nicknamed lo Stivale, meaning "the Boot", because its outline resembles a high-heeled boot. Three smaller peninsulas reinforce the shape: Calabria forms the Toe, Salento the Heel, and Gargano the Spur.
The Italian Peninsula contains most of Italy as well as the two enclaved microstates of San Marino and Vatican City. Italy accounts for virtually the entire peninsular area, while San Marino occupies roughly 61 square kilometers and Vatican City less than half a square kilometer inside Rome.
The Apennine Mountains form the backbone of the Italian Peninsula, running its full length from north to south. The range is so central to the landmass that one of the peninsula's formal names is the Apennine Peninsula.
Mount Vesuvius, located on the Italian Peninsula, is the only active volcano on the continental European mainland. No other country on the European continent has an active volcano within its territory.
In the strictest geographic definition, the Italian Peninsula begins south of a line running from the Magra to the Rubicon rivers, just north of the Tuscan-Emilian Apennines. This boundary excludes the Po Valley and the southern slopes of the Alps.
The Italian portion of the peninsula is home to more than 26 million people. San Marino adds around 31,000 residents and Vatican City around 829, bringing the full peninsular population above 26 million when all three political entities are counted.