The Key is one of 201 treasures in Pikmin 2. In order to obtain it, Olimar must go to Sublevel 5 in the Citadel of Spiders located in Perplexing Pool. Use your yellows to defeat the Beady Long Legs and get The Key, worth one hundred Pokos. It unlocks challenge mode. In challenge mode, Olimar must find the key on each sublevel to open up holes and eventually escape the challenge.