Make your way to the old factory in garbage region its actually easier to sneak in through a small gap in the southwest wall than fight your way through. Once inside, immediately take the stairs down and watch for patrols, they're pretty predictable if you're patient. The lab entrance needs code 2605 on the keypad near where the stairs end, but definitely grab some anti-electrical gear first since the place is filled with nasty anomalies.

Might be worth knowing that bloodsuckers love ambushing near the entrance, so keep that shotgun ready and save before going in. Fighting works too if you're geared up but you'll deal with endless reinforcements, which is just annoying when stealth is simpler. Pack at least three medkits and maybe some artifacts for the electrical stuff, and you'll have a much better time handling whatever's waiting down there.

The lab equipment is pretty unstable too so watch for random discharges, they hurt way more than you'd expect and catching you off guard is kinda their thing.