Check everything (at least briefly) before touching anything, then? (The laboratories and work rooms sound most likely to have usable information, though there might be something worth poking in preservation or mortuary...)

Seems prudent. This place looks like it hasn't been touched in ages.

She adds what they find on to a new section of their map. 

Then, once everything is at least sketched out: "Poke Lab One first?" It looks empty - gutted, really - but it makes as much sense as anything to poke them in detail in numerical order. 

"I'd rather start with one there's actually something left of. Two, maybe."

She nods. "Works for me." Onwards to Lab Two. 

Lab Two is labeled TRANSFERENCE/WINNOWING. Inside, it's divided into two separate rooms, IMAGING and RESPONSE respectively. The door to RESPONSE is locked. Through the circular window in the door, the room looks empty apart from a pedestal against the back wall. There's some kind of box or object sitting on it.

IMAGING is unlocked, and has a little more going on. There are big banks of defunct machinery, purpose uncertain. Empty bookshelves, a rusty metal desk. In the center, a pristine metal podium, with a flat plate of dark glass on top of it.

The podium crackles and hums like it's getting ready to start when Ellyn gets near it.

Does it do anything interesting when Gideon approaches? 

Nope. There's an faint outline like a handprint on the glass.

She touches it. 

Nothing happens.

"Maybe it needs to be a necromancer?"

She'll step back so Ellyn can try. 

When she puts her hand on the glass, a solid metal shell extends down from the ceiling around where she stands at the podium, down to about her waist.

Does anything else happen? 

A tone from outside that might indicate the other door was unlocked.

She goes to check it out.

RESPONSE can indeed be opened now. That is, until it shuts abruptly.

Ellyn pokes her head out of IMAGING.

She relays what she saw. "Might be a challenge just for the cavalier? Require the necromancer to be entirely in another room to have the door work. ...Though if so, they forgot about bone adepts." 

"Could be. The screen retracted when I took my hand off the pad, and I think the door relocked at the same time. I want to try sending a construct in first, if you can watch and see what happens."

She nods and goes to stand in front of the window into RESPONSE.

Ellyn sets a skeleton up then goes to stand in IMAGING again.

The skeleton enters when the door opens, and it closes again after. As the skeleton moves towards the back pedestal, a monstrously massive bone construct grows out of the far wall and powderizes Ellyn's construct before it makes it more than a quarter of the way across, quickly shrinking again when there is no other movement in the chamber.

She relays this! And: "I want to fight it."