If some group held a black mass in secret, no one would know about it. Officially, nothing of that sort ever has happened.
Vatican Council I was the first Ecumenical Council to be held at the Vatican in Vatican City which is an independent country.
It was held in Vatican City from 1962-1965.
People do not select the pope. He is chosen by the College of Cardinals in a secret conclave held in the Sistine Chapel in the Vatican.
Most sessions were held in the Vatican and at other locations in Rome and Italy.
You become a pope when you are elected as such in a secret conclave held in the Sistine Chapel of the Vatican to replace a pope who as either died or retired.
The pope is chosen by the cardinal electors, all cardinals under age 80, in a secret conclave held in Vatican City.
The council was held mostly at the Vatican but some meetings were held at other venues in and around Rome.
This occurred with great regularity and frequency in the past half-century, after the 2nd Vatican Council of 1965 decreed that masses no longer had to be held in Latin only.
In Vatican City, thus the name Vatican Council II.
The First Vatican Council was held in Rome, Italy in the Basilica of St. John Lateran.
in Rome
It was held 1869-70.