There are 3 maps with 4 subtypes each. Some subtypes have persistent trapdoor location, others have a lot of random locations.
Trap door becomes visible when at least 2 generators are repaired. It opens when you are the last survivor on the map. It has loud opening sound. Opened trap sounds like open tunnel.
If killer stands on trap door it doesnt spawn until killer moves. You can body block any trap door if you stay one step from opposite side of door.

suffocation pit (long building with pit inside)
near long building, at the end with window
DIdn't make screenshot, but the spot is pretty visible
ironworks of misery (huge industrial building)
inside of two-story industial building, on the opposite side from generator


shelter woods (no places to juke, big tree in the middle of the map)
can be anywhere: between two trees, between stones, in ruins

coal tower (two-story building with generator and chest on second floor)
behind two-story building; not sure if this spot is persistent

torment creek (zeppelin wreck)
near zeppelin wreck, on the side of wooden part

rotten fields (no places to hide, endless cornfield)
can be anywhere. Notable spots: near harvester, near sacrifical tree with cows and pigs

Thompson's house (big two story buiding with chest and generator on second floor)
in dead end in terrace of 2-story building

rancid abbatoir (big slaughterhouse)
can be anywhere, same spots as rotten fileds + inside slaughterhouse, under dead cows

azarov's resting place (small building with sign on top of it with window in room and window near front door)
multiple spots. Knows options: near small house with basement, near building with window in room (can be either behind or in front)


wretched shop (big building with 3 windows on one side)
behind big building with 3 windows in a row

blood lodge (two-story building with ramp inside and generator on terrace)
Inside two-story building.

wrecker's yard (no buildings other than kiler's house)
can be anywhere