Gideon's already entirely naked, so any extra offense is probably a moot point. 

Fine, fine.

Anything stand out when she gets to the latch?

There's definitely some kind of latent ward on the blade - but it's tiny, the size alone making it incredibly hard to analyze, and quite possibly deeply encrypted.

Hm. This is a stupid thing to do, but-

This is the Ninth study. This is their Saint, the hidden one, the one who kept Tamerlane safe. She wants to know what was locked away on the First.

Ellyn cuts herself on the warded razor.

It's gossamer thin at its edge - the sharpest she's ever touched, possibly, and it parts her skin without pain. As her blood touches that tiny ward...

There's a subtle flare of thanergy, and the mortar between the tiles - which is made of bones, miniscule fragments of ancient bones that were already long dead when worked into every square millimeter of this study - becomes apparent to Ellyn's senses, a moment before it curls away, an ancient construct politely pulling aside tiles made not of ceramic but keratin over a core of bone.

It has next to zero leakage - every motion is smooth, perfectly balanced, perfectly optimized for the barest whisper of thanergy in a dying drop of blood. 

The hole it reveals leads to further dark water - all-consumingly dark, and bracingly frigid. (To a long term inhabitant of the Ninth; anyone else would likely be severely affected by the rush of icy water.)

Just your everyday priceless Anastasian relic, sure. (Ellyn is definitely geeking out a little. There's like three of similar things left on the Ninth from the time of their founder, constructed entirely out of oss so subtly that you can't tell unless you already know.)

Into the tunnel.

Gideon first? 

She is the stronger swimmer.

She ducks in - checks for anything obvious like a gap right above the tunnel leading to an immediate room (no luck), realizes there isn't a notable current, then pauses, reconsiders, and indicates they should surface for air.

Once above water: "We don't know how long that tunnel is, or if there's any dead ends. Can you like - make some kind of sac with air or something in case I need an emergency breath? Like divers use in the comics. And I want you to stay out of the water, monitor me with transference, in case I need a rescue - it'll be a lot easier if you're fresh and can move quickly to my location, or summon a construct through my eyes, rather than if you've been crawling along behind me, slowly running out of air."

"If you think that's necessary."

Ellyn will make Gideon a skin bladder for air, and get set to spin up transference.

"Don't know for sure, is the issue. And it'd be really stupid to drown after we've gotten so far."

"When you're ready, then."

She gets ready quickly, taking a few deep breaths before diving in. 

She has to feel her way along the tunnel - the lack of current continues, which means the exit should be above her, at the same level as the pool she entered through - though the tunnel itself isn't perfectly straight, with sharp bends and a few short dead ends - Gideon does her best to move quickly, contorting through areas that seem better suited to a snake than a human - she's slowed down mostly by the dead ends, though - by the time she's breached the surface, she's had to take several breaths from the swim bladder, and to lean on her own great endurance, but Ellyn should be able to make it now that she knows the exact path to follow. (Assuming she's been taking notes.)

The room she emerges into is small - cozy - there's even a towel for her to dry herself with, preserved down the years by strong wards. (The towel is organic, made of human tissue - hard to tell which ones through transference - and has its own wards woven into its very structure.)

"Think this is a library," Gideon says out loud, trailing her fingers over the dense writing on the walls - finding collections of exceptionally thin bone tablets carved with further words - far more durable than flimsy or even paper. (Far less dense a way to store information, though; the tablets are only inscribed on one side, and are several times thicker than the thickest paper Ellyn has ever had the priviledge of handling.)

Ellyn catches up a few minutes later.

"This would have taken- years."

"The Lyctors were here for a very long time - but... Anastasia must've lived for way more than a normal human lifespan." Proves the rest of the Houses wrong about whether Anastasia deserves her title as a Saint. 

"Mhm."

What are the writings about?

Her own experiments with perfected Lyctorhood, sounds like - 

- And an inscription:

You who have kept the Tomb, who have kept faith, do you know what it is we guard? Do you know the Truth of who God is? I have sworn never to speak of that final Mystery, never to whisper it to my descendants - but the Emperor, may She continue to keep Her glorious head out of Her blessed ass even after I am gone, did not think to say anything about inscriptions in my own private study. 

If you truly have kept the faith - activate the ward encrypted beneath this. 

"This means us... right?"

"It should... Though - she must've come back here after the Tomb was built." The rest of what they've found hints of an era for predates the Tomb, often significantly.

And decrypting that ward requires knowledge buried in some of the Ninth's oldest books - 

- Fortunately among the ones Gideon just about memorized.

It won't be fast, necessarily, especially without pen and flimsy - but she's pretty sure she can decrypt this, with Ellyn's help on the aspects only visible to necromancers.

The bone tablet trick is not too hard to replicate, now that she's seen it done.

That'll cut some time off.

She can't let Gideon do it all by herself.

They do their best work together, after all.