You don't want to know.......
It is horrid. The only thing I hold against my grandparents.
From Wikipedia:
Lutefisk is dried whitefish (normally cod, but ling is also used) treated with lye. The first step is soaking the stockfish in cold water for five to six days (with the water changed daily). The saturated stockfish is then soaked in an unchanged solution of cold water and lye for an additional two days. The fish swells during this soaking, and its protein content decreases by more than 50 percent, producing a jelly-like consistency. When this treatment is finished, the fish (saturated with lye) is caustic, with a pH value of 11–12. To make the fish edible, a final treatment of yet another four to six days of soaking in cold water (also changed daily) is needed. Eventually, the lutefisk is ready to be cooked.
It is eaten with massive amounts of melted butter.