How create another subdirectory where ghost is already installed

I gotta say, this one is mystifying me too. I’d like to create a subdirectory to run wordpress (it has handy plugins ghost does not) thus: https://ghostblog.tld/wordpress

The Nginx tutorial you referenced above is not clear, nor can I find any ghost documentation on how to create a subdirectory that can operate independent of ghost.

Thanks for the help.