3 Demigods in Trouble bonus (Patreon)

Percy, Jason and Nico wonder into a cave looking for a monster, only to find out too late that the cave is the monster, with its own magical immune system.

Still they make a nice sculpture in its stony stomach. The mystical waters leeching away at their life essence to sustain its pool till they are nothing but solid cold lifeless stone and even that is eroded in time till there is nothing left but an echo in the monstrous cave.