Ott's Assay Office on Main Street is one of the authentic Gold Rush commercial buildings in Nevada City, dating to the 1850s. An assay office was essential to any mining town: it was where ore was tested for its gold and silver content, and where the value of a miner's haul was officially certified.
The building is a good example of the brick commercial architecture that replaced Nevada City's original wooden structures after the fires of the 1850s. It's listed on the National Register of Historic Places and forms part of the concentration of historic buildings along Main Street that makes Nevada City's downtown such a coherent time-capsule of the Gold Rush era. The exterior is the draw — interior access is limited.