![[TBTS-waterelemental.jpg]] *As the narrow corridor comes to an end it opens into a massive, natural cavern. The corridor empties onto a small stone embankment, and a lake of water laps at its edges. A beam of solid starlight comes down from the ceiling above and spills onto a tall alabaster pillar at the center of the room. The light illuminates the cavern and throws dancing shapes across the walls that reflect out of the crystalline idol of a hippopotamus, which sits atop the pillar. Two large, flat stone islands jut above the water’s surface on either side of the pillar. Two simple boats made of wood and reeds, each with a set of oars, sit on the edge of the embankment.* The water here is 10 feet deep and each boat holds up to 3 Medium creatures. **Islands.** The stone islands are smooth and slippery. If a creature moves more than half its speed while on an island, it must succeed on a DC 13 Dexterity saving throw or fall prone. If a creature takes the Dash action while moving on the island, it has disadvantage on the saving throw. **Creature.** A water elemental lurks in the lake. It follows beneath the characters as they swim or boat to the islands or pillar, and it attacks them when a character attempts to climb the pillar or touch or grab the idol. When it rises out of the water, it looks like a giant hippopotamus, and its slam attacks look like bites from the creature’s watery jaws. It focuses its attacks on the creature that is closest to the idol, trying to stop them at all costs. If it can’t reach the creature closest to the idol, it focuses on the creature that appears to be the biggest threat to the idol’s safety. **Rough Waves.** As the characters cross the lake, the water elemental attempts to disrupt their progress when they get within 15 feet of an island. It subtly pulls at them or their boats by manipulating the nearby water. The water elemental can affect only one boat or swimming creature at a time. If the water elemental targets a boat, each creature in the boat must succeed on a DC 15 Dexterity saving throw or be thrown overboard. If the creature using the oars succeeds on a DC 15 Strength (Athletics) check, the creatures on board have advantage on the saving throw. If the water elemental targets a swimming creature, the creature must succeed on a DC 15 Strength (Athletics) check or be pulled underwater for 1 round. **Retrieving the Idol.** The pillar is 5 feet in diameter, rises 50 feet out of the water, and is very slippery. Each round a creature spends climbing the pillar, it must succeed on a DC 13 Strength (Athletics) check or slide 10 feet downward. If a creature fails the check by 5 or more, it loses its grip on the pillar and falls into the water below. The crystalline idol weighs 10 pounds and is warm to the touch.