Vatican Secret Archives, Vatican
Containing important state papers, correspondence, papal account books, and many other significant documents which the church has accumulated over the centuries, the Vatican Secret Archives are among the most forbidden places in the world. In fact, it was not until 1881 when Pope Leo XIII finally allowed at least some researchers to view some of the contents. These days, only highly qualified scholars may apply for entry. Even then, there are very strict limitations to what accepted scholars can actually view.