Generic high-fantasy setting (d&d 5e if you want to use specific spells), what security or defences would mages use to secure the place where they keep all their magical stuff? I’m thinking decoys, reinforced and hidden location, guards (hired or summoned), locks (both magical and mundane), booby traps, and spells to discourage or confuse passing snoopers.
Also it’s going to vary depending on the resources of the wizard and of the players. Is this an independent student wizard protecting their studies that a low-level party could reasonably break into, or is it the king’s secure vault of confiscated magical horrors that’s a final boss for the campaign?
I’m looking for ideas for fun obstacles, and critically that the players can’t just sidestep with a single low-level spell!
What I did in an old C&S campaign was purloined lettered the Hell out of the lab.
The PCs invaded the wizard’s keep. They quickly searched the grounds, kicking down doors and making sure all the guards were subdued before hitting the main tower. There they fought their way up the tower to where the most defended room in the keep was. After disabling most (not all!) of the traps, magickal and physical both on the entrance way, and taking their lumps for the traps they missed, they broke into the proper lab, all filled with glassware and books and components and braziers and whatnot.
Only to have it turn out that everything in there was common and useless stuff glamoured up to seem important until you touched it.
In the mean time, while the PCs were being kept busy in the keep’s tower, the wizard came out of the basement crudely hidden under straw in the stables with all his most valuable stuff packed and carried out of the grounds to a safe distance before he triggered the final trap that turned the tower into a towering inferno.
The fools hadn’t even rolled to check for anything in the stables; I mean it was just the place where the horses were kept, right…?