Black Hole (Pikmin: Sinister Incinerator)

The Final Dark Spore
After the President's rescue from the G-Base in the Penumbra Plains the President will help Olimar and Louie activate a large destroyer machine nearby the G-Base entrance. After you find the scattered batteries around the area and input them into the machine's sockets, it'll fly to a certain area of the plains and demolish a huge boulder blocking the way to the Black Hole, which holds the final Dark Spore and is the last of the dark caves. Prepare the perfect Pikmin force and give yourself a full day to trek across the plains to reach the Black Hole at the distant corner. You're in for a 20 floor dungeon, the second longest in the game. You're going to be fighting on pretty much every floor (mainly for keys) of this ancient crater to reach the bottom where you'll face off against an ultimate force of a final floor boss. If you manage to defeat it, then your Research Pod will neutralize the threats of all six Dark Spores then and there! Now you must gather the remaining treasures out of 300 that you might have missed, which should all be fairly obviously located by now. After you get 300, you're free to leave the planet- but not quite. As you fly upwards, your Research Pod will detect the source of the machine-corrupting spores, faintly emanating from a strange place known as the Portal. This is the last area, where you must try to discover exactly what was spreading those spores, and why it needed the dark spores.