How to unlock: talk to Fred Allen in Rexford hotel at the reception (or in the basement) in Goodneighbor
After talking with Fred you will receive a smaller quest of obtaining halluciGens for him from the HalluciGen, Inc. factory. Inside, a battle between mercenaries will take place. This will give you many opportunities to sneak up undetected and kill from hiding. The time works for your favor as the members of the factions are killing each other.
Only one straight road through the building leads to the underground laboratory. You can enter the room on the right before the last door locked with electric lock. In the terminal you will find administrator password to that terminal (and behind the drawer - a minigun).
In the last room you will find the leader. Despite the fact that he is not a boss, he is quite a strong opponent (and he is able to become invisible). Laser trap is lying at the entrance, so be careful. In the last laboratory room you can collect 9 canisters of the HalluciGen.
Hint: HalluciGen canisters (full) can be used for crafting unique grenades (the containers are very rare), so collect them all.
Quest rewards: experience, 200-400 bottlecaps (the questgiver requires only one canister)