Griffith Observatory’s major expansion did not simply add a new building beside its familiar domes. During the renovation that closed the observatory in 2002, new space was created underground while the Art Deco exterior was retained. The project restored the building, replaced the aging planetarium dome, and added new exhibits and the Leonard Nimoy Event Horizon Theater. It reopened in 2006. By placing much of the growth below ground, the renovation expanded the public experience without replacing the hilltop silhouette visitors already knew. Source: https://en.wikipedia.org/wiki/Griffith_Observatory?oldformat=true
Source: Griffith Observatory, official institutional history of the 2002–2006 renovation and expansion; Wikipedia, “Griffith Observatory”