The phrase "innermost parts" typically refers to the most private or hidden parts of something, whether that's a physical object or an emotional state. There are a variety of synonyms that can be used to convey a similar meaning, such as "depths," "core," "heart," "center," or "soul." These words suggest a level of intimacy and vulnerability, indicating that the subject in question is something deeply personal or significant. Other synonyms might include "most hidden," "most secret," or "most private," all of which capture the idea that the innermost parts of something are often the most sacred or sensitive.