Launch Facility is the only secret level of L.A. Meltdown in Duke Nukem 3D. It is accessible from Toxic Dump and The Abyss. It can be reached from The Abyss even if the player has already entered and completed the level via the Toxic Dump hidden button. This map is not a secret level in Duke Nukem 64, as it follows Toxic Dump.
1. After you get the blue keycard go back to the slime pond room. Go for a nice swim and after making your way through a short passageway you'll be in a small-enclosed area with some shotgun ammo and two atomic health atoms. Make sure to click the slightly brighter wall in here for some chaingun ammo.
2. In the room with an atomic health atom sitting on a platform, right above the RPG there, is a fan in the ceiling. Bash the fan in and jetpack up to snag some pipe bombs.
3. In the small computer room with all the pig cops and the red keycard, a section of wall opposite the switch opens the missile launch room doors and reveals some armor.
4. After you've destroyed the missile and taken cover underground you will find a main computer console. In the room with the switch that opens the passageway and leads to the exit, jump up onto the console and push the screen. It opens and reveals three atomic health atoms.