Uncle Theodore

And special thanks for mentioning Zone Manager! I'll definitely look into this plugin, it looks like it's a convenient tool to use any PVE events even in the vanilla Rust. Also perfect for more complex events like my Puzzle Houses.

Regarding loot as a reward for players, unfortunately, I could not come up with an adequate way for a player to receive a reward only once. I do not know how to solve this with the standard tools of the game, apparently, a special plugin should be used for this.

You can get auto-authorisation when pasting the building -- just add "auth true" to the /paste command. The cupboard for the labyrinth  hidden in the walled column, just a little bit straight from the entrance.

Changed Status from Pending to Not a Bug

Did you get building authorization? That should give you full access, including the mailbox.
(Sorry, I'm not familiar with Zone Manager — is it some kind of plugin?)

The building was thoroughly checked — I'm sure all the wallpapers were intact initially.
(Maybe some went missing after a server restart?)

I usually leave the boxes in the throne room empty so that admins can manually add the most suitable loot.

Yes, after that horses will align to the Hitch & Trough and start to eat.

Honestly speaking I don't get it what the doors are you talking about and who are "they"? Can you please describe what kind of issue do you have?

Changed Status from Pending to Fixed

Alas I'm not familiar how the Simple PVE work (for sure it is possible to change the horse ownership to you somehow). However as straightforward solution you could spawn a new set of horses inside the room. Console commands: to remove the horse "ent kill", to spawn a horse "entity.spawn ridablehorse".

Sorry, I didn't fully understand the problem -- you are the admin and have full access to the room 4B, right? Because to start horses to eat you should simply sit on them once, to align them to the Hitch & Trough (the food already loaded). Or SimplePVE blocking you from the horse ownership even if you have admin permits?

Changed Status from Pending to Closed

Sure, the clue for the first entrance code is inside the rules itself (see, the fourth paragraph). The code for the all entrance doors is the same.