There are many, many people with this problem begging for help in forums.
Here's one with a wide variety of ideas, many of which ended up being suggestions that I could incorporate, at least partially:https://answers.microsoft.com/en-us/windows/forum/windows_7-files/very-large-temporary-internet-files-cant/7f09329b-e4fd-4386-bdea-f23689c05799
I tried messing around in these directories in safe mode with a command line. I very tentatively tried using del /f/s/q and it seemed good. It prints out messages for each file deleted which I found helpful rather than trying to send it to > null (or nul?) It turns out that the hidden Content.IE5 folder didn't have a whole lot of files in it.
I had a bit of a panic trying to get out of safe mode, but when I did CTRL-Shift-ESC to start the Task Manager I was able to find the Log Out button, and when it went back to the safemode log in screen there was a restart option. https://www.google.com/search?q=how+to+exit+safe+mode+with+command+prompt&rlz=1C1CHBD_enUS730US730&oq=how+to+exit+safe+mode+with+command+prompt&aqs=chrome..69i57j0l5.9337j0j7&sourceid=chrome&ie=UTF-8
There was a folder called "Virtualized" which seemed to have a mirror of the windows directory tree and seemed to have some large files. A bit of research seemed to indicate that this is for caches that older programs used to save outside the user's directory that's not allowed anymore. And these can be safely deleted, so I did it.
This has some explanations although it's a bit brief: https://answers.microsoft.com/en-us/windows/forum/windows_7-performance/virtualized-folder-in-temporary-internet-files/34b442ce-0036-44d5-85ae-00ec39971298
Here is a lot more information which provides better reassurances that it would be ok to delete these files: https://answers.microsoft.com/en-us/windows/forum/all/virtualized-temporary-internet-files-eating-up/828a81bb-a11e-4c23-b033-316cfb638f3a
The previous link provided greater reassurances for trying TreeView, which turned out to be AWESOME. I checked it out, downloaded it, and immediately it showed me that the files were actually hiding in AppData\Local\Microsoft\Windows\Temporary Internet Files\Low. It didn't seem to have any problem finding hidden directories in its scans. I gave clearing the temporary internet files one last try, then did a big del /f/s/q and that fixed it.
The instructions on clearing temporary internet files from the control panel. It did seem to something but didn't touch the 30Gbyte: https://community.f-secure.com/t5/Common-topics/Cleaning-temporary-Internet/ta-p/18280
Where to get Treeview: https://www.jam-software.com/treesize_free/features.shtml
