California's beautiful Presidio, located within the Golden Gate Recreation Area at the entry to San Francisco Bay, saw continuous use as a military base for 218 years by the Spanish, Mexican, and American armies. The building houses some of the oldest walls ever built in the city. At the heart of the Presidio, these walls make up the structure called the Officers' Club. After the original adobe walls were built by the Spanish colonists in 1815, they went into hiding starting in the 1880's when a new layer of wood was added.