Iceberg Lake is a lake in the Land of Ooo notable for icebergs which drift in and around it. The icebergs generally are eternally frozen unless unfrozen by someone who has a means to melt them. Within many of the icebergs are various debris possibly from a former civilization that was annihilated during the Mushroom War. However, certain beings that could survive within the icebergs are also frozen within them, such as a platoon of Businessmen which somehow survived and drifted through the lake for a long period until Finn unfroze them and subsequently refroze them.
The lake initially appeared in "Business Time" as the location where Finn and Jake decide to build a Gauntlet Dock, initially without success until their discovery of the Businessmen in the lake, which they unfroze and assisted them in making the gauntlet better. After stopping the Businessmen, they were refrozen in an iceberg and sent back into Iceberg Lake.
The lake also reappears in "Mortal Folly", where it's location was revealed to be on a border area between the Candy Kingdom and a chaotic area where The Lich's Lair resides on the other side. As The Lich headed forth to reclaim its power, Finn and Jake were forced to cross it to stop it, all while being pursued by the Ice King who had captured Princess Bubblegum.