They find themselves alone in a circular chamber, perhaps 60ft across. The walls appear to be a tangle of gnarled branches and vines stretching upward, as they were in the passage. In the center of the room is a somewhat raised rim around a circular pond. It's maybe 2ft high and 15ft across. The cool illumination seems to be coming from the water within; a dappled blue-green light plays faintly across the room to the sound of gently moving water. A few archway-opening can be seen to lead away from this place into darkness...
What now?