Renovating Griffith Observatory, one of the architectural icons of Los Angeles, was a major feat of structural engineering. The rehabilitation of this 1930s icon featured new subterranean galleries, offices and workshops. Historic preservation requirements made it necessary to construct an underground basement. Our design included adding new exhibit and support spaces totaling 25,000 square feet to the existing building by extending and deepening the existing partial basement. This process required underpinning existing walls and columns, excavating new spaces under the main floor and constructing new columns and foundations at the required depth. Other modifications included new stairs and elevators within the existing building, a new hillside mechanical plant and modifying the existing planetarium floor. Miyamoto engineers developed a jacking procedure allowing loads from the existing structure to be transferred to the new framing without disturbance to existing historic finishes.