Crypt
Every church or basilica has its own crypt of some sort. St. Peter’s is not an exception. The main difference with this crypt is that it is not full of common people, or people with some status in the time they lived. This crypt is full of past Popes.
The other difference is that there are two different levels of crypt. The one level can be explored (no photos however) by walking down a small spiral staircase. It not only takes you pass the coffins of past Popes, tells when they lived and died, but at the end takes you past some of the original foundation stones of the church prior to the basilica.
The second crypt is much more difficult to see. It takes you down further for a more intimate connection of where St. Peter is buried. This level requires a tour guide, and these tours fill up months in advance; especially when there is a specific Catholic holiday. There are strict regulations on people’s age and dress when visiting the necropolis.
Entry is free. St. Peter’s Basilica is a church and appropriate clothing is required. Come in at least casual dress.