The World’s Longest Cruise, Viking sets sail from London on Sunday. The epic 245 days journey will span six continents, 51 countries, 111 ports and covering 55,700 nautical miles before returning to London in May 2020. The cruise Viking will also attempt to set the Guinness World Record for the “longest continuous passenger cruise,' according to a press release. The new record will be confirmed successful upon the return of Viking Sun to London next year by an official Adjudicator.