Yes, historic interior spaces can be considered historic, depending upon the criteria of the registration program and the reason the space is significant. The National and California Registers protect interior public spaces if they are historically significant (e.g. are a location where a significant event occurred) or have a design (for example, a theater) or character defining features (a firehouse pole) that contribute to understanding of the resource. Many local registration programs only protect exteriors, unless the interior is specifically addressed in the designation application.