"Yes. I'll probably have a sorcery school that's better at purifying things in about a week. Are there any magical effects you don't care about as much that sorcery can do? If I deemphasise them it'll be better at what it focuses on."

"Medicine and personal physical enhancement or alteration, we've pretty much got covered, if that helps."

"It does, yes. I'll work on something."

"Awesome.  So, shall we get that venom sample?"

"Where would you prefer me to put it?"

"Hmm.  We don't actually have a lot of glass around, but I bet my sealing coconuts beat your horrifying acid venom.  Come with me."

He leads Sadde to one of the giant coconuts hanging from the ceiling, which has a metal or metal-looking wireframe staircase next to it leading about halfway up its vertical diameter.  He knocks, three times, and a portion of the wall separates, slides inward, and is hoisted upward by internal vines.

The inside is white and vaguely glassy-looking, lit from above by a glob of white fungus.  Heavy-duty vines cluster on the ceiling, supporting the door just by its frame.  The floor is not concave, but flat and level with the doorway.  Shelves extend from the wall, apparently grown naturally.  They're lined with, mostly, more coconuts.  These ones are coconut-sized resting on circular frames; some have little labels pasted on them.  There's a few glass vessels on the wall as well, most of which wouldn't look out of place in an earthly chemistry set.

There's a table in the center of the room, also grown out of the floor, with instruments of chemistry made out of the same glassy white substance, a few plants in pots that might be some extremely magical pitcher-plant derivative, and half a coconut on another circular stand.

Zacharias grabs an unlabeled coconut and sort of twists it apart, so that without cracking it splits in half, just the way the giant one opened.  "I gotta go grab some Wellspring water.  You can stay here but don't touch anything."

He looks around and nods. "Okay. I'll wait. And I think your guess is correct, based on the texture of these things."

He leaves, and returns a few minutes later with a coconut-bowl full of Wellspring water, which he places inside a shallow glass bowl so that, if the sealing-coconut does get melted, the actual glass will catch the contaminated water.

"Right in here," he says, tapping the coconut.  "By, you know, whatever method you usually do this."

He sticks a finger in there. "Most vampires cannot do this. Perks of my witchcraft." Venom starts being poured from the finger.

The coconut turns out to be robust to, at least, diluted vampire venom.  "That should do it," Zacharias says after a few moments.

He stops.

"That's good."

He seals up the coconut, labels it with "vampire venom - extremely dangerous, irreversible transformation" plus several little skull-and-crossbones symbols, and places it on the shelf.  "I'll take a look at that.  Somebody'll set up a workroom for you to crank out some weapons," he waves his hand vaguely, "in a few days, probably.  I'll retool one of my sealing-rooms to hold some dragon flesh samples that we can test vampire bone against.  I can get that done today but it'll take a few hours, and I have nothing on the docket for you till then - you can head back to your room to relax or work on your sorcery school or whatever, or you can hang out here so I don't have to send someone to find you again, your call.  Ah, not here here - not inside the coconut, off in a corner of the lab."

"I think I'll return to the books and—read all of them."

"Works for me.  See you in a few hours."

He nods. Library!

Library!  If he tries to read all the books he'll get to read about Tairil's history, primarily tribes and warlords fighting for control of Wellsprings until a woman named Joanne (they don't seem to do last names in Tairil) discovered how to alter their properties, and leveraged this ability to take over the world, found the nation of Tairil Unified, and make everyone immortal.  He'll learn about architecture-magic, which is even slower and more unwieldy than Wellspring meditation; almost no one knows how it works anymore, you have to get an apprenticeship to learn about it, and it's only used for Gates between cities and the Sepulchres themselves.  He'll learn about dragons - the dangers of dragonblood contamination, the variety of breath weapons they've been known to use, the fact that lindworm hordes have been observed to use some small-scale tactics but nothing like strategy.  He will, if he's interested and he looks long enough, finally find a straightforward explanation of all the known draconic body plans.

He has about infinite patience. Or something approximating it. He's most interested in the lindworm tactics, the straightforward explanation of draconic body plans, and whatever there may be about the other kind of magic.

Lindworms seem to have a rudimentary instinctual understanding of battle tactics.  Absent any apparent outside instruction, a horde of attacking lindworms will organize themselves into squads and formations.  Lindworm hordes that are following a larger dragon will wait for their dragon to disrupt the defensive line from the air and then take advantage of that disruption.  Against larger forces they'll make use of hit-and-run guerilla tactics.  But they have no grasp of large scale strategy - lindworm hordes make no distinction between low-value and high-value targets, make no effort to conceal their movements from scouts, do not seem to comprehend things like supply lines as they apply to enemy forces.  When they took Tairil, they did it by dint of superior numbers and Tairil itself being almost completely unarmed at the start.

Dragons come in five main varieties.  Wyverns, the kind Sadde fought when he arrived, have two legs and two wings, and some manner of breath weapon.  After lindworms, they're the most common and weakest.  Amphitheres have more snakelike bodies than other dragons; they have two wings and no other limbs, and they're much faster than other types of dragons.  Instead of breath weapons, they usually have magic venom with strange effects.  Salamanders look like minuscule dragon embryos within soft translucent eggs; where wyverns have breath weapons, they have the ability to surround themselves with vast storms of matter or energy.  Hydras have no wings but multiple heads.  They heal from wounds supernaturally quickly, even more so than other types of dragons; whenever a wound heals, it grows another head, often with a new type of breath weapon.  Wyrms are much, much larger, rarer, more dangerous, and harder to kill than other dragons, long and sinuous with no limbs and the ability to levitate.

There is very little information to be found about architecture magic.  It seems to involve casting complex rituals over the materials of large structures as they're being built in order to imbue the final product with magical effects.  Learning enough about architecture magic to design something as powerful and complex as a Sepulchre would take multiple human lifetimes.

He's read stuff to the effect of the dragons' constitution like that elsewhere but always pretty oblique or just lightly described. It's good to have complete, detailed descriptions like that, and of course he memorises all of them.

Who built the Sepulchres?