Get the "closest" property value

[George Mauer]

If I have a document what looks like the following. What code could I run
for the ??? to get the property value for "workspace-directory" that is
closest in the outline to the location running the code?

* Top Level
  :PROPERTIES:
  :workspace-directory: /tmp
  :END:

   #+begin_src emacs-lisp
     (???) ; /tmp
   #+end_src

** L2 Heading
   :PROPERTIES:
   :workspace-directory: ~/whatever
   :END:

   #+begin_src emacs-lisp
     (???) ; "~/whatever"
   #+end_src

** Another L2 Heading

   #+begin_src emacs-lisp
     (???) ; /tmp
   #+end_src