Are you talking about Legacy Dashboards?
As far as I can tell unless a dashboard was shared with you, you cannot access it... I've never seen an admin backend that allows me to see every dashboard that exists....
Back a few years ago, Dashboards that I know existed, and I had to rebuild, I had to ask the recipient to send me a copy so that I could see what was in it....
If you are actually talking about Workspaces, that is different... as an admin, you can open up the Workspaces area and expand filters... then you can expand "Other Filters" and select "Show All", this should you every single Workspace in your company... There is an export to CSV option, but I don't think there is a download option... you will have to open each one individually to download as far as I can tell....
