A chime will sound and a door, hidden elsewhere in the level, will open, leading to retro game heaven. To unlock a classic level, you need to first find a hidden lever and pull it.
They're a lot of nostalgic fun to explore, and there are no less than 13 - one in each level of the new game.
Like Wolfenstein before it, Doom 2016 has a particularly lavish kind of Easter egg: classic levels from the original Doom and Doom 2, recreated in the new engine in all their original low-resolution-texture, low-poly glory.
