On 22 April 1932 Maurits Escher leaves for Italy, together with his friend and painter Giuseppe Haas-Triverio. Their destination: Sicily. In Gangi, the duo is approached by a couple of street urchins, who ask them if they would like to see any dead priests. *
A large key was produced and, surrounded by a gang of shouting boys, Maurits and Giuseppe descend into the crypt of the Madre Church. Almost all the walls are pockmarked by rows of niches containing mummies. Escher took some photos and created this lithograph as soon as he got back home.
Source
[*] M.C. Escher, His Life and Complete Graphic Work, edited by J.L. Locher, Abradale Press, 1982, page 36