Where are all of the secrets in 'The Shores of Hell'?
There is a website called Classic Doom. It has information about maps and secrets for the PC and console versions ofUltimate Doom and Doom 2, as well as Master Levels, Final Doom and even Doom 64.
here's the link: http://www.classicdoom.com/
As for getting to the secret level, In E2M5, there should be a switch in one of the rooms that lifts up the floor into stairs and there should be a secret teleporter that should lead you into the secret exit.
I don't think that E2M8 has any secrets in the level, I believe, but I could be wrong.