The George Peabody Library contains one of the most beautiful rooms in America. The reading room is a six-storey atrium of cast-iron balconies stacked to a skylit roof, lined floor to ceiling with 300,000 volumes and absolutely silent. It is part of the Johns Hopkins University library system but open to the public on weekdays.
Access is free but controlled — you check in at the desk and are then left to stand in the space and look up. Photography is permitted and unavoidable. Events, including weddings, are held here, which means access can be restricted on some days. Check ahead, and if the dates align, this is one of the things worth building your Baltimore itinerary around.