AXDOOMER | The 16 secret stairs of E4M3 - The Ultimate Doom @AXDOOMER | Uploaded 10 years ago | Updated 17 hours ago
http://doomwiki.org/wiki/E4M3:_Sever_the_Wicked_%28Doom%29
There are 19 secrets beyond this door. There is one located right on the other side of the hidden door, then there is 16 of them that are stairs leading to 2 other sectors where a soulsphere can be found. This can be easily seen in ZDoom, because stepping in a secret sector will trigger a sound and a message centered on the screen.