If you stay long enough on the roofs and upper levels of Meridian Village (you can reach them by creative jumping), NPCs start appearing on the upper platforms.
If you see a broom on those platforms, there’s a good chance a NPC will appear after a little while if you’re on that level, and start using it, but they also appear where there is no broom. They don’t really do anything in that case, they just stand there or they pace back and forth.
But nothing is more unsettling than that random Oseram guy who stands on that roof next to the chimney and stares right at you without moving. (I’ve noticed there’s a broom on the level just under, so I guess that’s where he’s supposed to appear, but he is somehow glitching in the wrong place.)
Also, that guy changes as soon as it leaves your line of sight xD But every time, it’s an Oseram (for me at least).
This also happens in Lone Light. There’s a broom on a platform of the first building to the right, that spawns a npc if you linger long enough on the roofs there.
There’s also a broom (I think ?) on the second level of the inn in Daytower, and it also spawn a NPC, who uses the broom and also repairs stuff. Like the others, he only spawns if you manage to get up there.
No npc spawns on the upper levels of Meridian and this is just sad :(
(edit) Wait, let me amend that. There’s a place on the second levels of Meridian, near the Palace Gate, where I recently discovered a NPC during the side quest The Sun Shall Fall. He gets there because he is alerted to the glinthawks, but he was too far away to see if he was a Carja guard or an Oseram Vanguard.