The Ancient Cistern is the fourth Dungeon in Skyward Sword.
The Ancient Cistern is a tranquil, water-filled room with a Hindu-style statue dominating the central area. However, the same process which purifies water for the upper levels dumps sludge in the lower floors. Thus, the lower area is infested with Cursed Bokoblins, while the upper level features several water and fire-based enemies.
Contrary to prior water-based dungeons, the Ancient Cistern is generally puzzle-free, with the few puzzles there are featuring the massive Hindu statue in the center of the dungeon. The dungeon mini-boss, the Stalmaster, guards the Whip, which is then useful in conquering the rest of the dungeon. The Boss Key, the Blessed Idol, is contained in the polluted section of the dungeon, where it is guarded by Cursed Bokoblins. The dungeon boss rests in the highest portion of the dungeon, the Ancient Automaton, Koloktos.