Is the living worker in town, maybe we can ask him about the layout of the base
The worker(s) are still living in town, however asking them about the project seems a tricky prospect. Or rather, asking them any specifics about it seems difficult, as your cover is that of a researcher. You could probably make a good case for talking with them about their experiences on the project and what it was like, but if you started asking for details as to how the base was laid out, they might grow wary. There is also the inherent issue that the base has probably been updated and changed since they built it.
Still, some basic questions might reveal something interesting. Maybe some hidden way in?
Is there any convenient drainage pipe coming out of the base? Since we and our minions don't need to breathe, it might be a good entry point.
I say we just wait for the rats and birbwise to return. Just sort of put up the appearance of puttering about while we wait. Then go back to Esme with our new intel.
+1
You spend two days mostly just sitting around, practicing your ventriloquism. Despite hours upon hours of work, you still cannot manage to get any better at it. You're quite frustrated, honestly, that you have gone this long and tried this hard and made no, or at at least very minor, progress.
In the early morning hours of the third day, the rats begin to show up, one at a time crawling up the wall of the building and into the room. Once they're all in attendance you again get the piece of paper with the existing map out- as well as a few extras- and start making demands. First you have them draw out patrol routes; again these are just a list of "sightings" but you can draw lines between the static sights and plan out the routes from there. Next, you have them fill out what the purpose of each building is, as far as they can tell. Some are clear guesses but the majority are clearly marked. Storage, specimen storage, animate specimen storage, utility shed, main labs, barracks, secondary lab buildings, etc. One thing is out of place or at least unexpected: a section marked "Mass Grave".
This makes no sense for multiple reasons. First, there's a clearly marked incinerator on the edge of the property, so why would bodies be buried when they could be burned? Second, why would a necromancy facility dispose of bodies? Surely even the smallest scraps of flesh might have their use, unless they were simply too degraded. Even then, the incinerator should be their destination. All you can think is that at some point in the past the facility had far too many bodies to handle...but why?
Also included in the intel was information about drainage and ventilation. The ventilation info is essentially worthless, at least for infiltration purposes for someone your size. The vents are about the size of a shoebox and held together with screws, the points of which fill the vents like barbed wire. The drainage is slightly more viable, pipes about 2 feet in diameter, leading to various sections of the compound. However, some of the input pipes appear to significantly smaller than others.