Everything is easy, just break this wall of flesh

Eastern coridor of the hospital, it's behind the wall of flesh in the room right in front of one eyed moon.

Wall of flesh again. You can find it left from pressure control station (PSI selection).

Behind webbed pass, to clear the way you need to destroy all the moth eggs on this level.

Near the room with number 1 you can see talking head (???).
Look behind and on the right you can barely see passage, the key is there.

In the room with paintings come to the second floor and go on the rooftop.Then find a way to the coleseum.
Go down the road and you find a key (beware of 2 monsters).