I often use an outrageous photographer persona when trying to gain access to places I am not allowed, and that persona is super-bad-British-accent Benevius Throckmorton the Fourth, the National Geographic photographer who is too aloof to carry proper documentation and too aghast to understand why anyone would ask for such a thing.
You would be amazed that this persona has worked 100% of the time, and I get to take my camera into places where photographers are not normally allowed. The best place I infiltrated was the impervious Altar of the Duomo in Milan.
Below is a famous restaurant in Amsterdam that Benevius was allowed to photograph. This first picture is taken in an underground area where they keep all sorts of mysterious wines and meads that have been fermenting since the Renaissance. The second picture has some original Rembrandt sketches right above your dinner table.