I found a cave surrounding an underground lake. A narrow spit of rock jagged out over the lake and disappeared into the gloom. I wanted to investigate further, but it was getting close to the time the creatures normally appeared, and I felt exposed in the vast space. I found an alcove where I could hide and still be able to see the cave if I leaned out.
I'd dozed off, but was woken by the sound of chanting. It was the same sound I'd heard before, but now it was close. I leaned my head out of the alcove. Dozens of creatures stood around a fire near the lake, chanting in their horrible, rasping voices. One of them was walking slowly down the spit of rock, back toward the others. It was carrying something. It put it down next to the fire: it was a bowl containing a small amount of dark liquid. The creatures came to the bowl, one after another, and bowed to it, before taking a small sip. The chanting grew louder as each creature went to the bowl. When the final creature drank, the lake began to bubble. It felt like the whole cave was vibrating.
Something huge rose from the water, and my heart shot up to my throat before sinking down to hit my feet. I ran. I ran blindly, without thinking, directly away from the cave. I was lucky. I didn't run into any of the creatures. When I'd calmed down, I found a place to hide.
Nothing that big should be alive.