I'm looking for a good form for a stolen McGuffin that contains lore. It needs to be something that will last thousands of years in an environment that is cool and moist. The culture creating it is druid-centered and largely more primitive than most D&D cultures,  but they have some metalworking ability.

I'm thinking of either stone or clay tablets, but I'm open to something more fantastical if it sounds fitting. The McGuffin does not need to be easily portable as long as it fits into a bag of holding. Suggestions?

How about some kind of vision stone or crystal?

A druid-centered culture might save this lore in something more natural than written records - perhaps an egg that hatches into a creature that telepathically conveys the lore (or a seed that grows into such a plant). This potentially adds some complexity in figuring out how to get it to hatch, but might also explain why copies were not made as could happen with a book or scroll or some object carved with the information.

Or perhaps it's knowledge passed down unknowing to whatever heir of the original archdruid who held the lore; druids seem like an oral tradition kind of folk, but again if it's a McGuffin it has to be unique. So the heir does not know they hold this ancestral knowledge until the circumstances are right.

Magical stones or crystals as Shasarak suggested would also fit for druids.

A crystal. The words are read by holding a light source behind it and it projects the markings onto a wall or similar. It'd last basically forever regardless of environment.

You could make it a Cauldron of Knowledge, based on the legend of the Bard Taliesin and the Celtic goddess Ceridwen (link for wiki page). In order to acquire the knowledge provided by the cauldron, a potion must be brewed in it for a year and a day, and the first three drops from it ingested (the rest turns into poison). Obviously you could adapt it to your own setting and change the specifics using the legend as a general idea (which is a IRL Druidic legend). But the basic concept is that rather than the lore being read from a book, it is acquired by ingesting a potion that affects the user's mind like a drug, granting them insight.

I like rawma's suggestion about a natural creature.  What about something like a child Groot-like seedling from the druidic "knowledge" tree?

That would be small enough to dump into a bag of holding.

An ancient silver or bronze mirror, surrounded by glyphs from the druid-alphabet. If you can speak/activate the glyphs correctly, you can view the lore you want to see, though "as in a mirror, darkly".

Quote from: Chris24601;1115232A crystal. The words are read by holding a light source behind it and it projects the markings onto a wall or similar. It'd last basically forever regardless of environment.

I like this. Any examples of this in D&D already? Other mediums?

Quote from: Shasarak;1115235I like rawma's suggestion about a natural creature.  What about something like a child Groot-like seedling from the druidic "knowledge" tree?

That would be small enough to dump into a bag of holding.

Many living creatures die if you keep them in a bag of holding for more than a few minutes. OTOH, a stone golem could be an animate version of a stone tablet.

https://en.wikipedia.org/wiki/Cryptex

basically the maguffin from the Da Vinci code

Quote from: HappyDaze;1115238I like this. Any examples of this in D&D already? Other mediums?

They have something similar in The Atlas from Rise of the Tomb Raider, which projects a map when light hits the crystal. I'm pretty sure I've seen similar stuff from other sources, but my memory is mush.
https://tombraider.fandom.com/wiki/Atlas_(Artifact)

Quote from: HappyDaze;1115239Many living creatures die if you keep them in a bag of holding for more than a few minutes. OTOH, a stone golem could be an animate version of a stone tablet.

If you like some other creature, grant it the effect of a necklace of adaptation?

Megalithic astrological architechture with festivals and oral traditions attached. Y'know, just like earth! You can add magic by requiring a blood sacrifice to a festival ritual, making typical magic pyrotechnics.

How about a lacquered piece of wood with the information inscribed on it in a language or as artwork?

Gold or other metal tablets/sheets, a la the book of Mormon.