Hrgach notices a smell possibly what is making the hairs stand on end, its the smells like decay. The decaying smell is fait like it is far off and seems to be coming from the far wall of the cave. Inspecting the wall it appears to be hollow, perhaps a secret passage.
With a bit of searching you find a odd rock in the cave pressing it the wall slides open, revealing a staircase beneath. The smell gets stronger and the stairs are dark cut from the earth.