I agree, ncdu is a great and easy to use command line tool.

On Mac OS, run for example:

   ncdu -x --exclude /Volumes --exclude /System/Volumes /

This scans the root filesystem but excludes the Volume mounts specifically (the -x option to limit the scan to the current filesystem doesn't work properly on mac os). Navigate through the folders, sorted by size, from there. Press d to delete a folder.