Singing Squid, Astral Fish, and Uppity Iguanas

I've been using NASA's "Symphonies of the Planets" as white noise lately, and naturally, it turns one's thoughts to space whales and the like. So picture this:

A very large earth-gliding squid hides under a glade somewhere in the land of the skull, singing (in its primordial tongue) to lure astral fish down into its long tentacles. This siren song interferes with every dream, every "Sending" spell or telepathic link, and every divination passing near the glade. It isn't otherwise audible in the waking world. 

Within the glade stand about two dozen pillars of loosely-fitted stone. At dawn, anyone viewing the pillars from above can see that their shadows draw a large rune (part of a region-wide diagram which helps bind the skull). Anyone knowledgeable about stonework or quarrying will realize the pillars are centuries old, and the stones aren't local. (They were thrown here when the skull first broke the surface.)

At night, most pillars are topped by spiky masses. As the day warms, these masses unwind into iguanas, big as pandas and prickly as porcupines, who graze on the sharper fibers of the lichen (which they need for their spines). They consider themselves above interacting with humanoids - they were made intelligent and ageless by the moon before it died, and therefore consider angels and other higher beings to be their proper peers. Once adequately perturbed into speaking, an iguana will first try the ancient dead language of the moon, then passable draconic, and finally broken common. They cannot read.

Once every two or three days, a great invisible fish bumps into one of the squid's upstretched tentacles, and gets wrestled down into the earth. Several have escaped, and now wear the thorny hides of iguanas as protection and disguise. (The iguanas can't tell the difference and believe themselves immortal; they don't find claims to the contrary credible.) The cloaks weigh the fish down too much to return to astral space. They survive by eating the iguanas' dreams. 

The oldest and widest pillar predates the others. It contains a hollow, which contains a clay pot, which contains two fragile books packed securely in a desiccating powder. A wizard entrusted these books to the iguanas long ago for safekeeping. (The wizard was buried in the skull's original eruption and will not be returning.) One book, written in the lost language of the moon, concerns the anatomy of the soul and the stages of detachment during death. The other, written in the almost unknown language of the sun, chronicles the ascent of mortals to godhood. Scholarly types can translate them using a certain book of verse known to reside in a certain private or exclusive library. Both books are written in a maze-like manner, as though to confuse and trap the reader; anyone who reads them alone will find their possessions rearranged as though someone else had possessed their body in the interim.


Challenges

• A natural smooth-walled pit contains a wizened gnome. The iguanas shoved him in because he's genuinely awful. He wants the books and can't escape this oubliette without help.
• The iguanas will resist any attempt to remove the books or the gnome. With stern language if possible, and by shoving if not. They won't bite or claw unless attacked first. If seriously injured they'll try to topple one or more pillars onto their assailants. (If the shadow rune is damaged, a bear will come along in 2d6 days to help repair the pillars.)
• Anyone flying over the pillars or trying to enter (or exit) the astral plane may be attacked by invisible flying fish. The spike-cloaked fish will come to their fellows' aid (trying to nudge assailants into the tentacles), and the iguanas will come to the aid of what they believe to be other iguanas. The squid generally ignores things bumping into it at ground level, and assumes anything higher to be a delicious fish. 
• Killing the squid or extracting something from its gullet will be difficult because its body is safely underground. When someone casts a spell on the squid, it will retaliate with a spell of its own which, anytime the target tries to speak, makes its target gulp air instead of speaking. It's intelligent, but convincing it to stop singing, or to move elsewhere, or to cast some other rare spell for you will require a suitable gift of astral fish. (Teaching it new, high-level spell songs may also suffice.)

If the PCs just want to hang around for a few days to study the squid's song or the shadow rune, nobody will stop them. If the PCs have historical questions for the iguanas, the iguanas may grumble but they'll answer any polite question with whatever hearsay they can remember.

If the PCs manage to do some favor for the squid without asking a boon, it may reward them with a set of mystic squid eyes; applying them to the PC's own eyes causes the PC's pupils to split into three lobes, and grants both Darkvision and Brightvision (you can see 60 feet in any light which would blind most humans). If subsequent gifts are called for, it may offer small squid, or tentacles from mid-size squid.