The ARGON building is an office building located in Campo dei Frari.
At the time the Phantom is performing art heists, one of the suspects named Antonio Fango works in the ARGON building. Nancy Drew, an American sleuth enlisted to help the Italian GDiF, is stationed at the Ca' Nascosta, where Antonio's office is visible from the rooftop. Nancy uses this to her advantage to spy on Antonio whenever he's in the ARGON building.
Whenever Antonio leaves, Nancy can break into his office using nothing more than a simple bobby pin.