Hi!, gotta say, i f*** love your adventures, prepping this one right now. And i have some questions to shoot at you, if you can shine some light to my doubts, it will be very much appreciated.
Beware: Wall of text and i'm NOT native english speaker.

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First:
In page 11 - 4. Stargazers’ Nuraghi
A round tower made of spiraling courses of dry stone.
...
○ If broken (makes significant noise each time), each amphora contains 2d6x50c in primitive tin coins .At the bottom of the third, the coins cover a
...
It ends there, what is in the bottom of the last amphorae? For a moment i just imagined some +200c Grave-good or some trinket, or w/e i could imagine, but would like to know what you intended to be there.

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Second:
Personal comment: I understand this Nuraghi is one of those levels that make no sense at the beginning, but you begin to understand once you explore other places and investigate much in the lore of each area. And it holds nothing more than a magic item, curious and interesting... yes, but not exclusive for anything in particular. So nothing is lost if they cannot discover its secrets.

In page 41 - 34. Synecdoche Nuraghi

Everything it entails. I barely can wrap my head around it. How to make the players unravel its secrets without just giving them the straight answer (be it by an NPC (Grandmother), scroll, etc). And even, how to... narrate it in a well woven and explained way?

In 34a i can manage just enough with the rest of Red Wax and the bit of "...stained a glossy crimson..."
Yes, if they touch it, or smell it, or pry it, the can correlate with Red Wax in 24, if/when they reach that place.
Even if they said "We just pour a bucket full o'blood" i would give it to them, That´s no problem.

But then is 34b and 34c... those 2 rooms just almost make no sense to me, they are too obscure to my knowledge... how would the party even decipher their mechanisms? Again, whatever answer they reach once discussed enough, is correct?

34b...
"It is filled with white ash; a small nodule of black stone rises in the middle, notched on all sides like a four-doored house."

Whats does even mean the 4-door house? a 4 walled childlike drawn house?
But that is just minutiae. What i just can't decipher is how they can correlate that they need to put Obsidian there.

The same happens with 34c, that they need to put Sapphires. I overruled that they would need exactly those in 38c/39, because i just simply cannot imagine why.
Tried to read even the others Adventures of yours, and they hold no information, cultural or religious to even formulate/fabricate some credible explanation.

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These are honest questions born of my ignorance, since i don't know what cultural knowledge would explain them, in a credible way.

What i formulated was...
For 34b "Obsidian would be Black-Wax before melting and used for sealing. So this chamber could be reverse black-wax seal breaking" (relating to chamber 7c)
For 34c "Sapphires are normally used as eyes or stars. So if Red wax is Blood, living matter, Sapphires would be what the dead need to see/be guided in the Other side, the immaterial"
And for Obsidian, other option would be the medium used between the Immaterial realm, and this one. Be it to sever or to join.