Apple says that this space is hidden and not accessible to users, but I don't think it's like that. It must be stored some where, so where could this be stored?
To display /Volumes/com.apple.TimeMachine.localsnapshots in Finder in High Sierra or Mojave do the following:
• Hold the Command+Shift buttons then press on the . (dot) button
• This will enable the option to view hidden files
• Hold the Command button and press Space
• This will open the Spotlight search window
• Type /Volumes and press Enter
[To turn off viewing hidden files do Command + Shift + . (dot) a second time.]