Via Atlas Obscura:
Roman churches usually aren’t shy about their macabre histories. At Santa Maria dell’Orazione e Morte a nun will be happy to let you photograph their crypt of abandoned bodies in exchange for a small donation. At Santa Prassede a sacristan will give you a pamphlet and helpfully point out the well where St. Praxedis and St. Pudentiana poured the blood that seeped out of the three thousand bodies of martyrs they were hiding. At the famous Capuchin crypt you can even buy postcards of the mummified monks to send to dear friends or enemies.
But if you go to the Basilica San Giovanni Laterano looking for such morbid attractions, you’ll find you’re on your own. What happened there over one thousand years ago is still too horrible to speak of. This is the church where Pope Stephen VI put the rotting corpse of Pope Formosus on trial in January of 897.