Just around the corner from the Pantheon, a 16th century library is tucked away. It holds the collection of an Augustinian bishop Angelo Rocca (1545–1620), who had originally bequeathed his 20,000 volumes with the instruction that they should be made available to the public, regardless of wealth. By doing so, Europe’s first public library was founded in Rome.
In 1786, the reading hall (called the Salone Vanvitelliano) housing the collection was opened to the public. It holds 200,000 works, of which more than half were published between the 15th and 18th centuries.
The library reading hall is still open to the public. If you are popping just to see it, you are allowed to silently view the library from the entrance way. If you are interested in bringing something to work on and want to take advantage of the quiet space, bring an ID and the receptionist will help you fill out a quick form to permit you to sit at one of the desks for a while.
Rome is full of churches, temples, and other religious sanctuaries, but this is the quietest, and perhaps most spiritual spaces I visited while in the city.