So I'm running a Dark Sun game, and am working on a dungeon for the PC's to go through. After a particularly difficult opening encounter in the dungeon with a psionic spider and some undead, the hallway splits into 2 directions. To the left, they hear the faint howling of wind and smell smoke. To the right, they smell rotting flesh and acid.
If they continue to the left, they find the hallway absolutely LITTERED with skeletons and bodies, all of them in a position where their arms are outstretched in the direction of the hallway's entrance, with scratch or clawmarks on the ground from their hands. The skeletons/bodies also don't have anything below the waist, as in their legs are GONE. And the player's with high enough passive perception will notice that in some places on the walls or floor, be it etched in the stone or written in blood, there are warnings to “RUN!” and “STAY AWAY!” or something along those lines.
They also find broken weapons, wrecked armor, and discarded but useless gear of all kinds. If they continue down the hallway, they find a multi-headed reptilian beast with acid dripping from hits many maws, somehow chained into a big room at the end of the hallway that's just littered with bones.
In case you can't guess it, it's a hydra. And behind the hydra, there's a small fountain, maybe 5 feet across, with water in it. And around the spring is a pile of jewels and treasure. Hydras are level 10, the party is level 2.
With the bodies and the written warnings and the other signs, have I given my player's enough of a sign to tell them to not try to fight the hydra, and to just leave it be?