'Hákarl' is a national dish of Iceland consisting of a poisonous shark that is centuries old. Fermented shark has a strong ammonia-rich smell and fishy taste. The late Anthony Bourdain once described it as “the single worst, most disgusting and terrible tasting thing” that he had ever eaten, and Gordon Ramsay said he that "he couldn’t even swallow it".

They hunt the Greenland shark or other sleeper shark, clean and prepare it. Then, It’s first buried underground in a shallow pit and pressed with stones so the poisonous internal fluids that allow it to live in such cold waters can be drained out making the meat safe to eat. After its cured underground, they leave it hung to dry for four to five months.

Then, it is cut into small strips and served. With a smell that’s described as ammonia-rich and a strong ‘fishy-flavor, its a customary dish’. Those who have slightly more experience with 'hákarl' describe the experience as an unpleasant one at best, as the smell is something similar to ammonia, and the flavor is not much better.

Though it is a dish not many could bring themselves to sample, 'hákarl' is a meal rooted in history and tradition. When the earliest Icelandic residents settled on the island centuries ago, they eventually found the Greenland shark. Abundant in freezing waters, and measuring an average length of 24 feet (7.5 m) and a weight of 1700 lbs (771 kg), the shark was the perfect source of food.

More Info: en.wikipedia.org