That vault

That vault is one of the terminal entries located on the Tempest. It is a follow-up email sent by Cora after the founding of Prodromos on Eos during A Better Beginning. There are two versions; which one is sent depends on whether Cora was on the squad in the Eos vault.

Text, Cora in Eos vault
"To: Ryder

From: Cora

Can still smell that Remnant vault on my armor. Lot of weird shit down there. Like my huntress manuals would say, "the razor's edge between known and unknown teaches you what can be cut away."

Now I think back, it reminded me a little bit of some of the temples on Thessia. Same huge spaces and running "water." Same sense of a huge purpose you can't really understand. Makes me wonder if we'll ever really know what their builders did there.

Cora."

Text, Cora not in Eos vault
"To: Ryder

From: Cora

Read all the reports about the Remnant vault. Sounds dangerous as hell. You keep being just lucky enough. My huntress manuals would say, "luck is a balance beam between you and the enemy." But are the Remnant even our enemies, like the kett? Or just defending what's theirs?

Passed on a warning to Bradley and the others at Prodromos—not enough to scare them, just so they know what they might be mining down into. If SAM's estimates are right, that vault could stretch under most of the continental shelf. Makes you wonder. What could dig a hole that big?

Cora."