K. Lumsy's Prison
K. Lumsy Island is the small island that the giant Kremling K. Lumsy is trapped in for most of Donkey Kong 64.
After leaving his treehouse, Donkey Kong decided to swim over to and investigate the large mechanical island King K. Rool had parked next to Donkey Kong Island. Climbing onto K. Lumsy's Island, Donkey ventured inside of it and found the giant Kremling in his equally giant cage.
Seeing he had a visitor, K. Lumsy decided to tell DK his sad story. After he had refused an order to attack Donkey Kong Island, King K. Rool had K. Lumsy exiled to a small island towed behind the larger, mechanical one. After hearing this story, Donkey Kong, being the kind-hearted ape he is, decided to help K. Lumsy escape. Hearing that Donkey Kong was going to help him caused the giant reptile to jump for joy; all this commotion caused the entrance to the game's first area, Jungle Japes, to open.
After defeating every boss in the game (minus King Krusha K. Rool), the Kongs will be awarded with a large key which can be used to take one of the eight locks off K. Lumsy's cage. After freeing K. Lumsy of his prison and shutting down K. Rool's Blast-O-Matic, a short cutscene of K. Lumsy leaving his island and knocking K. Rool's unnamed airship out of the sky will be shown. Also, when the Kongs defeat King Krusha K. Rool, he will be sent flying, courtesy of Funky Kong and a rocket-launcher. K. Rool will crash land on K. Lumsy's Island where he is apparently beaten to a pulp by an angry K. Lumsy (who is back on the island without explanation).
The island is fairly unremarkable, though it does contain two Golden Bananas on it. The first Golden Banana can only be accessed with Lanky Kong and his Grape Shooter. The second is inside the island and is only obtainable by using Lanky and his special move Orangstand Sprint.