From the Super Mario Wiki
The Spanish Steps are a set of stairs near the Trinità dei Monti church and the Spanish Embassy to the Holy See (and not Vatican City as the pamphlet says) that lends its name to the landmark. It is also one of two landmarks in Rome, alongside the Pantheon, that are exclusive to the PC version of Mario is Missing!. It is also one of the five locations within Rome that get attacked by Koopa Troopas; they take one of the two Bannisters, causing the entire stairs to be closed. Luigi allows the steps to be reopened by grabbing back the Bannister and returning it to its rightful place, although the clerk at the information booth verifies the Bannister's authenticity first by asking Luigi some questions. These include:
The Spanish Steps and the piazza (plaza) it encompasses were actually built with French, not Spanish, money. The steps and the plaza take their misleading names from the Spanish Embassy to the Vatican. Wide and comfortably curved, these twin staircases are famous for their popularity with sunbathers, skateboards and tourists. The famous poet, Keats, once lived nearby.