The Chapel Royal of St. Peter ad Vincula ("St. Peter in chains") is the parish church of the Tower of London. It is situated within the Tower's Inner Ward and dates from 1520. It is a Royal Peculiar. The name refers to St. Peter's imprisonment under Herod Agrippa in Jerusalem. The Chapel is probably best known as the burial place of some of the most famous prisoners executed at the Tower, including Anne Boleyn, Catherine Howard, Lady Jane Grey, Thomas Cromwell, Thomas More and John Fisher. (Wikipedia)
At the time of my visit I understood there were a few crypts in plain view where important figures were interred. But, I had no idea that we were literally in a cemetery of no small number of burials. Here is a fascinating article with a map of the burial positions within St. Peter ad Vincula.