On 9 August 1957, Escher boarded the s.s. Luna, which was being loaded at the Surinamekade in Amsterdam. He was to spend over six weeks on board of this freighter, travelling to and across the Mediterranean, passing through a number of ports in Greece.
Escher had become addicted to traveling on cargo ships.
‘I tell all kinds of people about it, but only a seasoned cargo boat passenger can understand what I’m talking about. And you never (or rarely) meet those people on land.’*
The next day it was inclement weather. Waves of 6-7 meters rolled around the ship, but Escher sat on deck all day. He enjoyed himself intensely. Returning on September 23, he paid for his drinks during the trip: 11 whiskey sodas, 19 glasses of beer, 3 glasses of Bols, 18.40 Dutch guilders in total. He was not really a drinking person. The sea was (almost) enough.
Source
[*] Wim Hazeu, M.C. Escher, Een biografie, Meulenhoff, 1998, page. 387