Vatican Library
The Vatican Library is teeming with secrets as it is closed to the general public. Its most interesting part is the Apostolic Archive. It was separated from the main "collection" in the 17th century and contains letters written and received by popes and all acts promulgated by the Holy See.

The oldest document is a single parchment page dating from 809, which speaks of donations to the church in Venice. The archive contains a papal bull of 1521 on the excommunication of Martin Luther, as well as a letter from Henry VIII asking for a divorce from his wife. The verdict denying the request prompted the King of England to set up his own church, where divorce was accepted.

The value of the archive is that it keeps historical documents for more than 1200 years. An endless number of cryptic documents in different languages ​​are neatly arranged on shelves stretching for miles. Only academic researchers are allowed in, which is only a couple of thousand people a year. Based on this, it is safe to assume that there remains a huge amount of material that no one even tried to read.