You can tell u got the right exit if it is actually 3d and shows that there is some sort of block over the ceiling block in the elevator.
You should end up in a map with purple-ish textures.
Good guid

The prologue map has a 2nd secret elevator which leads to another map above the first prolog map. Check around the exit for hidden doors.

are the secret rooms also in the maps? i think in the first one they're missing...

you should type the name of the mission but that guide helps also but it would be better with wolfenstein the old blood mission map names

Still don't know where to find them all .Helpful Guide tho