'A' is in the garden on the 'on the roof' level. When you are on the roof with the three small balconies with doors and a large garden, drop down onto a ladge that runs along 1 and a half sides, use your batgrapple to reach a hidden ledge.
Envelope B
'B' is on one of the first crates in 'The Bridge', to get to it, climb the first ladder, and glide around the obstructing crate, then make a simple jump/glide.
Envelope C
'C' is in plant electrocution 2, fall down into the second hole on the long ramp, get a secret key, grapple out, slide the rest of the way down and open the first door on the left.
Envelope D
'D' is near the valve which lowers the third floodgate in 'Gasworks', there's rushing sluge coming out of a large tube, there are several floating boxes, jump along them to find 'D', this is very difficult for most people.
Envelope E
'E' is in the 'Swat chase' level, go down the elevator shaft and break the power box at the bottom, go into the door which opens, directly above you, not at the top. Take the secret key, ride the elevator to the top of the building and open the door.
