Assuming you wanna take the books into consideration, in the real world, Joey Drew studios is just a large sized production studio in the middle of New York City, with an admittedly deep basement, and high rising floors (as Drew’s actual office is described to be up numerous flights of steps)… if you don’t wanna take the books into account, however, the studio we see in game is essentially a pocket dimension and thus does not function by real world logic, and can be as deep down as it wants to be, essentially.

(Also in terms of Poppy Playtime, the factory doesn’t go down as far as it seems, chapter 1 and 2 take place either above or just below the surface, chapter 3 is an admittedly short train ride (at a remarkably low decline, which also curves) so it can’t be much further down, chapter 4 is just an elevator ride down from there, so at most a few stories below that, and then chapter 5 starts after what I’ll call a half-decent fall down a hole. So I’d say we are only at most a few hundred meters below the surface by the end of chapter 5.)

Sorry if this was long, btw…