I say we got all the information we could hope to get, so now it's time for us to actually do the thing and investigate the lab. First of all, we need to plan the route we will take to get there as well as consider alternative escape routes. Second is to actually choose our targets. Based on what we know so far, I'd suggest going through the sewers, finding an opening or creating one with a crowbar or screwdriver or whatever and then making our way to either the lab or that secret underground section. We take piecewise with us for muscle, carry a bunch of rats on us for disposable scouts/distractions and have birdwise on standby nearby. Would something like that work?
Also, I just thought of something: if we're undead would people other necromancers be able to tell we're undead? This could be bad if they can.
You see no sign of being undead in the mirror. You have no circular thread, and you even have what looks to be a normal connection to the anima, just like everyone else. They could tell if they touched you though; because you're physically clearly not alive.
You start tracing paths on the map, moving the pencil tip slowly through pipes and between buildings, planning a path. Piecewise coming with you is somewhat of a detriment, at least when it comes to moving through the sewers. Unmodified he was flexible but built up as he is, he's rather bulky. You do a quick measurement of his shoulders and then scratch off any route that his girth precludes. After going through each possible route, tallying up things like possible escape routes and guard paths intersected, you believe you've come up with the best route. The one you've selected starts to the side of the base, at a drainage pipe. You'll need some way to cut off the grate that blocks its end, but from there you can crawl up it to a nexus of pipes and then climb a ladder up to a maintenence access point. From there you're just one patrol path away from either of your destinations.
Escape routes are always a bit harder; obviously the major one is the way you got in, but you also make sure to memorize secondary routes as well as "Fuck it, I'm running" ways out for if things get really out of hand. Once all this is written out on the map it is quite a mess of arrows, and scribbled routes, but you commit the entire thing to memory regardless.
The route is planned, all thats left now is to actually do it. You think you should head into the woods before sunset, so that you can get into position and then move into the base whenever you think it best. You wonder about what equipment you should bring and, looking down at yourself, how you should dress. A disguise? Armor?