.7z is a high-compression file format created by 7-Zip, designed to hold large amounts of data, including images, text, or executables.

Without more context regarding where this file came from (e.g., a specific YouTube video, ARG forum, or download link), it is not possible to determine its exact contents or password.

Files with names like "Diamonds" or "Secrets" are commonly used in community-driven mysteries or game communities.

If you provide context—such as the site where you found it—I may be able to help identify the mystery or ARG it belongs to. Minecraft's greatest mystery was just solved!