Absent the occasional police car or fire engine appearing at its top, outwardly MIT’s Great Dome has remained as it was since 1916, a symbol of the classical ideals of education and excellence amid the industrial bustle of Cambridge. Inside was a different story. Plans to build the Boston area’s largest assembly hall in the dome were scrapped in favor of a more affordable library. Its spectacular 27-foot oculus was blacked out during World War II and obscured by pipework and drop ceilings for decades after. Renovated in 2013, the reading room is now open around the clock.