Hey so I've been going through and taking notes on the boys' lair so I can remake it in the Sims and I'm just gonna dump 'em all here for easy access and in case anyone else wants to use them :) Sorry this is gonna be long.
Also first off, this is just according to my knowledge + observations from the show, so if I've missed any information, feel free to add on or correct me! And second, there are several inconsistencies throughout the show that I'll do my best to mention, but for the most part I'll be going with the rooms/layout that is used most consistently and prominently.
As a note, I will be referring to the side that is most often viewed by the camera as the north side just to keep things oriented in the same direction.
Main hub spanning all 4 floors, connects to most rooms of the lair
Skate ramps across E/W sides, going from the second floor to the first. W ramp graffiti usually says "Donnie" and E ramp says "Pizza" though these change often.
("The Longest Fight" 1:23, above screenshot) Contains all the boys' bedrooms in each corner. Center area is surrounded by a moat. The only floor that is shown relatively clearly from all angles.
NW = Raph's room; shown with weight lifting bench in the background of shots. Shows up probably the most often out of all of their rooms.
NE = Leo's room; sword + cinder blocks + curtain, usually the only room with a curtain (or anything in the doorway for that matter), though Donnie's room is shown with one once ("Mind Meld" 9:08).
SW = Donnie's room; his and Mikey's rooms are shown far less often/clearly than Raph and Leo's but it seems to be located directly across from Raph's room ("The Purple Jacket" 6:18).
SE = Mikey's room; seems to be located across from Leo's room and the arcade ("Flushed but Never Forgotten" 2:47).
S = ???; fifth doorway usually dark in wide shots. Led to a room with a ton of boxes + a table ("Sparring Partner" 15:49). Used as an exit to the surface by SHELLDON ("Breaking Purple" 3:20). Unclear where exactly it leads.
N = Arcade; wide rectangular garage-like door. Usually the most prominent doorway in the backgrounds of scenes.
E = Splinter's room; round shoji door. Sometimes changes to rectangular in the background of shots, but always shown as round when interacted with.
Wide shot of Splinter's room as an extra since it's rare ("Insane in the Mama Train" 9:17)
Weird stair structure, basketball hoop on edge of walkway, and "Yo! Mikey" graffiti between Splinter's room and arcade doorways ("Insane in the Mama Train" 8:24)
S = ???; round sealed door ("Shreddy or Not" 14:42, I know it shows up in other scenes but I can't remember any of them for the life of me). Unknown what's inside.
W = ???; doorway with party garland strung across it. Possibly the kitchen by process of elimination since Raph is seen throwing Shredder through a wall from the arcade straight into the kitchen ("Shreddy or Not" 19:00). Shredder also looks and jumps upwards toward Karai who was in Donnie's lab, suggesting that the kitchen is somewhere downstairs from the lab which is on the third floor.
SE = possible 5th doorway? Shown right next to Splinter's room, opposite from the arcade. Usually square with no garlands. Used by Leo once to enter the sewer tunnels and track down Piebald ("Flushed but Never Forgotten" 8:19) so it's possibly one of the tunnels that leads out of the main lair area and into the sewers.
NE = Honestly seems to constantly switch between the projector room and Donnie's lab?? It's more often the lab just because that room tends to be more relevant, but anytime the projector room is shown, it also takes this spot. This doorway is usually shown in wide shots with a cluster of screens on the wall (likely representing the lab), but will sometimes change to the projector room entryway in establishing shots when the scene calls for it.
NW = ???, sometimes dark but often shown in wide shots with a small squiggle of string lights + some box-like object right by the doorway. Unknown what's inside.
Large "Turtle Power" graffiti and basketball hoop on a pole between these two doorways, right above the arcade. Basketball hoop on edge of walkway right in front of NW doorway.
Unknown what is on the south side of this floor.
Usually only ever viewed from below. Does contain a catwalk that characters will sometimes cross as well as a large fan and box like structure on the north side. Unclear what is on this floor otherwise.
Currently Unaccounted For:
Tank garage; although characters are frequently shown entering/exiting this room, it's unclear where it is in relation to any other rooms. Frankenfoot appeared on 4th floor bridge after exiting the garage, but he could have wandered around the lair beforehand ("Sparring Partner" 15:20). It's also not unlikely that it could be located on one of the upper floors since those are closer to street level. Has at least one large garage door entrance ("Sparring Partner" 11:46 + "Cloak and Swaggart" 11:05) and one smaller wooden door entrance ("Man vs Sewer" 11:11) as well as several large tunnels lining the walls ("Sparring Partner" 12:03 + several scenes in "Cloak and Swaggart").
Comic book safe; ("Jupiter Jim Ahoy" 12:48) possibly in/near Donnie's lab judging solely by aesthetics and amount of security, but it's never confirmed. Only appears in this episode.
Bathroom #1; looks like a normal bathroom, includes shower with curtain ("Bullhop" 14:13). Only appears in this episode for about 4 seconds. (thank you to the wiki for reminding me of its existence)
Bathroom #2; looks like a dingy public bathroom with several sinks along one wall, a shower with curtain, and a makeshift toilet made from a sewer pipe, which Piebald was flushed down ("Flushed but Never Forgotten" 1:56). Only appears in this episode.
???; honestly no clue what this room is, but the boys/Splinter were using it to prepare for their band performance ("Al Be Back" 13:28). Only appears in this episode. (thank you again to the wiki, i didn't even know this room existed)
Sewer tunnels; characters are rarely shown entering/exiting the tunnels from any other rooms, but it's likely that sewer scenes (such as in "Man vs Sewer" and "Lair Games") just take place in random sections of the rest of NYC's sewer system and therefore do not have a solid layout.
Aaaand that's about all I got. And since I realize this post may be hard to follow solely through text descriptions, I drew out my own mental map of the main areas for convenience. It's likely not 100% accurate (as is the rest of this post) so take it with a grain of salt, but this is what I'll personally be following:
Thanks for reading through this and hope it helps! :) Have a strawberry for your troubles 🍓
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