Wilderness Setpiece - Temple of the Great Eye

This comes from a /tg thread where I decided to write this setpiece inspired by a Conan adventure. I didn't make anything of it at first, but I finally decided to add it to my hexcrawl because a most generous anon provided an amazing picture of it when I asked, so I'm posting it here, all cleaned up.

Wilderness Setpiece: Temple of the Great Eye

• Hex Terrain: Desert
• Location: A 80x80 black stone temple with four pillars at each corner supporting a decorated ceiling with an opening in the center that's aligned with the full moon (when it's there). In the center is a 15x15 hole that seems to be bottomless. 
• Ceiling and columns: Depict various life episode under the look of a huge eye. Some of them depict animal and human sacrifice made to the eye. 
• Hole: The bottomless hole is about 100 feet deep. At the bottom is a huge cavern with some skeletons, bodies and leftovers. Around the cavern you can find: a treasure (roll as per a dragon hoard) and the Great Eye, sleeping on 1-5 outside of a full moon. It is very sensitive to light and will wake up. During the full moon, it is fully awaken, but calm and waiting near the hole.  
• Sacrifice: Every full moon, a group of neutral cultist comes here to appease the Great Eye with a human sacrifice (they bleed the victim and then throw it down the hole) and treasures. They are adamant on performing the sacrifice and anybody that gets in their way will automatically be considered hostile. If the sacrifice is not performed, the Great Eye will wake up and furiously destroy his cavern to emerge from the sand on the surface to wreck havoc. 
• The Great Eye: A gargantuan 9 HD chaos hydra (9 heads) with a special Death Gaze and only one huge eye on its belly (no eyes on the hydra's head). 
• Random Encounters (1d6):
• 1 - Desert devils (1d3, count as hostile air elemental)
• 2 to 3 - Nomand Brigands (2d6, count as brigands; they have a lvl 1d3 magic user (dervish) if they are 10 or more; never hostile to cultist; never approach more than 1 mile the Temple; superstitious)
• 4 to 5 - Arid zombies (1d6, the dead on the hex never stays dead for long because of the dark energy of the Temple)
• 6 - Cultist patrols (2d6, count as normal men; they have a lvl 1d3 cleric with them if they are 10 or more; they patrol the area to make sure nobody tempers with the temple)