first one, go to the room with the mimic chest and climb the platforms to top left, once you get it, there'll be a hidden button in the far left wall to escape, dont go through the door.
second one, the first room you meet where hands come out the walls, bait the giant doll into chasing you then get grabbed by the hands to avoid it. then escape and go to the door it came out of for a gear. find the corresponding gear and it'll drop down a chest in the room where you got the golden key from
third one, go right off start, stand on the stool onto a bookcase to unlock the closed portal, go through it. go far right, stack up the boxes on top of each other to the right, then kick the table from the right, she'll start chasing you but she cant go past the boxes. then throw the top box to the left so she cant chase you there either, grab the battery and power the robot right outside. then click the button on top of the stool to turn the portal blue, leads to key.