Original: Maderno's last work at St. Peter's was to design a crypt-like space or "Confessio" under the dome, where the Cardinals and other privileged persons could descend in order to be nearer the burial place of the apostle.
Simplified: Maderna's last work at St. Peter's was to design a sunken crypt called the "Confessio" under the dome, where people can go to be nearer the burial place of the apostle.