This isn't so much a museum as a collection of murals dotted around the Quadraro neighbourhood in the city’s southern suburbs. Works by nearly two dozen international street artists adorn the quarter's walls, ranging from a creepy 'baby Hulk' to a Modigliani-style nude and a striking display of crawling wasps on Via del Monte del Grano. Titled Nido di Vespe (Wasp's Nest), this creation by Roman artist Lucamaleonte is a reference to the name given to the district by Rome's Nazi occupiers in WWII.
A good place to start is with the concentration of murals along the walls of Via dei Lentuli. You can fully explore the murals with a Google map from the Muro website, but to get the best out of the area, take one of the regular guided tours on foot or by bicycle – see the website for details.