The two upper portals lead into a vestibule where there is staircase with 86 steps which leads to the Holy Cave, the very heart of the sanctuary, where the four apparitions of St. Michael took place.
The staircase ends with a portal with twisted columns resting on two lions, called the "Door of the Bull," after the large fresco above it depicting the episode of the first apparition.
Beneath the fresco is an inscription welcoming the faithful to the holy place: "This is the Crypt of St. Michael the Archangel, celebrated throughout the world, where he deigned to appear to men. Oh pilgrim, when throwing yourself to the ground, worship these stones since the place where you are, is a holy place."