How to delete a folder which is nested quite deep and to avoid “File name too long”?

To delete the directory tree starting at c:\subdir\more\offending_dir:

The total step-by-step-process is as simple as this:

cd c:\subdir\more to cd into its parent directory.
mkdir empty to create an empty directory.
robocopy empty offending_dir /mir to mirror the empty directory into the offending one.
After some waiting you’re done! Finish it up with:
rmdir offending_dir to get rid of the now empty offending directory and
rmdir empty to get rid of your intermediate empty directory.