An illustrated event cover for the Pompeii exhibit at the Royal Academy of Arts. The exhibit ran from Nov 20 1976-Feb 27 1977. But according to the below cancel, it appears to have been extended? 

Here is a last day pseudo-cancel that was applied to same cover as above, "...Posted on last day of Pompeii Exhibition" dated March 14th 1977. 
Thank you Tiem! A Pompeii view on center 2002 Vienna UN administration stamps
The sender of the card stated the obvious and wrote in 1929, "Pompeii on this picture was certainly old."