As others have said, ask nicely and ideally outside meal times and the crew will likely let you up the stairs and have a look from the back galley.
Again, as said, it's a small cabin so there isn't anywhere to "have a look around" and it would be just like a visitor having a look around the F cabin (ignoring the fact that they would be a "lower cabin pax") - there isn't really anywhere to go apart from looking at it from the back and those pax on the UD won't know (or care) that you are traveling in F so won't be impressed if you do a royal visit with a good look around.