Heretic's secret exits

Started playing this piece of gold again :)
Can anyone point me to what levels the secrets is in and where in the maps too. Thanks. (btw, I would like to know the secret exits in all 5episodes)

Episode 1 - near the end of map 6.
Episode 2 - a passage behind the Phoenix Rod in map 4
Episode 3 - in the area with all the Iron Liches in the water in map 4
Episode 4 - about a quarter of map 4 is secret
Episode 5 - behind the bars near the Ophidian tower in map 4

Thanks. :)

They seem to be obsessed with ExM4 :P