The Project Archives are available for the Team, Ultimate, and Enterprise editions and can be found in Setup under the Tools section.
Here, you can mark one or more projects (including filtered views) and Archive them. Such projects can no longer be accessed and can only be viewed here. However, by using the Restore button in the Archive itself, projects can be restored back into the list of projects and accessed again.
Archived projects are subject to the Data Storage policy and will be deleted accordingly.