Mission Found Argent Facility (Destroyed)
Access the Map
Look for the octagonal platform on the right near the start of the mission. Jump over to the upper platform and search behind the cargo to find the lever. Activate it and return to the previous walkway. Turn around and hop down to level 1 to find the entrance to the Classic Map.
Map Strategy
The second map of DOOM II is also fairly straightforward. From the start, go left to unlock the path, then follow the water to the right. Fight your way through Possessed Soldiers and Security until you reach a room with holes in two corners. Drop into the left one to find the blue key. Return to the water and enter the blue door across the corridor.
