If You Were a Wizard, How Would You Store Your MacGuffin?

[Dr paradox]

Heya. I'm designing a castle that used to belong to a Wizard. The players are trying to stop an Oni from plundering the MacGuffin inside. I'm looking for evocative ways the wizard might have secured this object, which is an irregularly shaped heavy metal case a little more than a foot cubed.

Feel free to just use that as the prompt, but for more details, here are the caveats:

Spoiler: CAVEATS

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• The vault is not totally watertight. Liquid must be free to seep down out of it.
• The vault is located on the third or so floor of a castle, immediately above the great hall.
• The wizard who secured it was fifteenth level at most (D&D 5e rules). You don't need to adhere to RAW or anything, I'm a big fan of esoteric wizard stuff, just giving you an idea of relative power.
• The wizard who built the vault has been dead for about two years, with her former prisoners occupying the castle. The vault's security must have remained relatively intact for that time without maintenance.

And if you really want the context...

Spoiler: CONTEXT

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In my setting, Trolls aren't exactly a species: they're more like an infection derived from some unknown giant in the distant past. If a humanoid is infused with blood directly from a Troll's heart, they gain regeneration, increased strength, and heightened pain tolerance, but they will eventually lose their mind and become a troll. A high price to pay, but in this region of the world, there is a tradition of berserkers who accept this practical death-sentence in exchange for a few years of martial prowess. So far, nobody has reliably been able to make use of a fully-transformed troll in a military context: they just don't care, no matter how much you pay them, and they will eventually start eating their allies or wander off to the mountains.

To feed this demand, learned folk will capture a troll, belt it down, and laboriously extract their still-beating heart from their body before securing it in a container that prevents the Troll from regenerating. If done properly, this produces what's called an Undying Heart, from which a practically unlimited amount of Troll Heart Blood can be taken. It's difficult to make and fairly easy to kill, so there aren't many of them, but those who have them can command a high price for access.

Among these was the wizard Tasya of the Four Chambers, whose Undying Heart was renowned for produced better results and slower transformations than other leading brands. She moved into a decrepit castle and set up shop, using mercenaries to abduct test-subjects so she could improve her methods while supplying local warmasters with all the berserkers they could find volunteers for. A village grew up in the shadow of the castle called Tasyagrad, and the fortress itself was named Krovzamok, also called the Castle of Monsters. Tasya turned the great hall into a large laboratory, and secured her Undying Heart in an enchanted vault above it, with a chain she could pull to pierce the heart anew and siphon the blood she needed without risking the heart's theft or destruction.

She went on accruing a fortune and conducting her experiments for another forty years, until one of her test subjects finally broke her neck in an inattentive moment. The rest of her prisoners were freed and butchered the rest of the castle staff. Several trolls broke free and attacked Tasyagrad down the hill, forcing the villagers to abandon their homes and leaving the whole place a ruined wreck. The test subjects remained in the castle, infecting first Tasya's apprentice and then whatever physicians or magicians they could abduct with the Troll Blood in the hopes of finding a cure for their affliction. It's been two years since the uprising, and many of the test subjects have completed their transformations and been locked in the dungeons again in the hopes they might be saved when a cure is found - though the possibility is starting to look remote indeed.

Now, an Oni pirate known as the Demon of Kharkel has been sent by his pirate fleet to buy or steal the Undying Heart for their benefit. The party, being opposed to that fleet, wants to thwart his plans and interrogate him on the fleet's next move. Along the way, they may try to retrieve the heart, either to bait the Oni into attacking them directly, or to hand over to the test subjects to improve their research, or to destroy to keep from falling into the wrong hands. Because of this, I ought to know exactly how it's protected.

I look forward to your ideas!

[vasilidor]

The vault is hidden behind a bookcase, the bookcase does not move and you have to physically pull the books off the shelf. There is a lead liner to prevent detection spells from working. If a person touches the box without saying the correct word it gets teleported away(the box, not the person). directly across from it is a dummy cache, covered in wards and things that would kill a person if they looked at them the wrong way. inside of that is a purple ooze. yes, the one that eats people. getting into the room would require people to get past an illusionary fire with a false riddle to drink a potion to get through. all the bottles have a lethal poison in them, with the insides of the bottles having a lead liner to prevent detection spells from working. directly behind the illusionary fire is a spiked pit about 10 feet deep covered by yet another illusion. there is another ooze in there that sits and waits for food to come to it. the pit is an empty space between two walls on the floor below.

[Pauly]

Important question
Did the wizard who secured it need to access it regularly?
If it’s essentially a bank vault holding something you check on once a year then you can go to town with elaborate security measures.

However, if it’s something to be accessed on a daily or weekly basis then the security measures will be more elegant. For example a lock that only unlocks when a specific low level spell is cast on it. A detailed example: the lock made of the usual fantasy unobtanium that is indestructible is a sliding puzzle box design. The catch is that there is an imp living inside the lock who keeps moving it around and preventing anyone unlocking it. The unobtanium is impervious to magic. The imp was trained to come to the only opening and bite a finger and feed on the blood. The imp will only stay still while Ghoul Touch is incanted. Casting GT on the imp causes it to become comatose for a minute, after which it revives. Cast any other spell and the imp skips out of range before it can be cast. The puzzle lock takes nearly a minute to manipulate into the open position. So to open the lock you need to know (a) that ghoul touch is required (b) be able to cast that spell while an imp bites on your finger and (c) how to unlock the puzzle box in the correct order.

[Telok]

The hearts-box isn't in the vault. What's in there is a glorified bucket with "keep blood fresh" spells on it and a tap. Its behing a false wall in an empty cabinet in an old disused kitchen. The whole upper floor is covered with a version of the old 'guards & wards' spell, that does nothing but make a mess of the hallways.

A couple years after the town sprang up the caster killed the blacksmith and replaced him with a simraculum (maybe cast from a scroll). The actual heart-box is under a stone block that the old blacksmith's anvil sits on. The caster would cast a simple disguise spell, take a bucket of broken iron tools to the blacksmith, and bring back a bucket of blood. The only evidence of this is a bucket of broken iron tools (intentionally broken on a weld, they stopped scrounging old tools early on and just re-broke & welded the same ones for years) that turns liquids invisible while they're in it.

Also the simraculum of the blacksmith is still hanging around the wreck of the forge. It dotters around on its last 3 hp looking freshly troll smacked. Its orders don't allow it to indicate in any way the existance of the heart-box or admit that anything is wrong. It will steadfastly maintain that the wrecked forge is in good condition, its not badly hurt, and that theres a temporary slump in business that will be over as soon as people "stop fussing".

[Mutazoia]

The MacGuffin is inside a 10x10 room with no doors or windows, the walls and the MacGuffin itself are warded against scrying/detection spells. The only way into the room is a tiny pinhole in the ceiling of the main hall, through which the wizard would pass using the Gaseous Form spell. The pinhole is just behind/under one of the bolts holding a chandelier in place. The ceiling is 50' off the ground. One would have to either know exactly where the pinhole was or spend hours crawling across the ceiling while removing any and all bolts/screws/nails to find it.

[Mastikator]

Inside the vault is a major permanent illusion that leads you to falsely pick up the wrong MacGuffin.

The major illusion is masked by Nystrul's Magic Aura to appear non-magical.

The vault also contains several (hidden inside the illusion) glyphs of warding that reactivate the illusion and the aura if dispel magic is used. Glyph of Warding is bypassed if *The Right Person™ (whoever that is, I didn't read the context) dispel magic.

Only a very high investigation check or a large series of high level dispel magic can defeat the vault if you're not the right person.

*if it's supposed to be blocked from everyone then skip the right person bit.

[Lorka]

With such a great setup I would use a Gelantious Cube that 'guards' the box. The box is suspended inside the Cube. The Cube is obviously mutated because of the constantly seeping troll heart blood, so it regenerate, maybe it's intelligent, I am also thinking pseudopods with or with out acid dripping claws. It's also basically invisible.

So that's what's inside the vault. Since there is a lot of experiments and bio-magic, the vault door might also be a troll blood infused Mimic, or the whole vault is the mimic with the Gelantious Cube inside it.

Maybe the Mimic Vault is hanging from some mutated Ropers, that can then use the Vault like a giant flail.

This larger room with Roper suspended Mimic Vault is then full of Troll Stirges.

I would amp up the whole bio-magic aspects and have loads of weird troll blood infused monstrosities.

[Tarmor]

It's not in a vault. It's in an extra-dimensional space (like a bag of holding) hidden somewhere else in a little used place under a flagstone or similar. Almost impossible to detect, but accessible if you know where to look.
Of course, if it's hidden properly, neither the Oni nor the players will likely find it.

If it's not meant to be easily accessible, but findable, I like the Gelatinous cube idea, or a Ochre Jelly in a pit, with a non-degradable container.

[Wraith]

Go full-on Indiana Jones And The Last Crusade. They make it into the vault and find not one, but scores of hearts in various types of cages, jars, buckets, aquarium, bowls and sealed glass spheres. All of them are beating, leaking gore across the shelves, and infused with every sort of magic that you think could possibly apply.

The hearts are all permenantly affixed into place - trying to remove them will smash their glass container and destroy them, so all you can do is take a sample of blood and hope you got the right one. And if you didn't... Well, we all know how that scene ended.

Do your characters know enough about exobiology to know their troll's heart from an ogre's? How about a diseased gnoll? Or a mimic that imitated a troll, was then killed in that form and quickly preserved? And even if they do, how long will it take them to figure it out while the alarms are going off and the magical traps start firing in their faces, and all of the other measures that have been mentioned above piled on top of each other?

[Quertus]

Depends.

Hide it in another reality?

Create a golem around it?

Store it inside myself?

Wield it openly, but as part of something else?

Store it in a lead-lines vault? No, not as part of the treasure, but actually inside the walls of the vault.

Store it outside time?

So, let's combine those a bit: store it as part of the walls of a lead-lined vault that exists outside time on another Tahiti l reality. Wield one part of the key openly, and place a portal to that reality inside a golem built for that purpose.

[Corey]

Part of the answer:

Something that resembles Leomund's Secret Chest, but with the small material component sufficiently different from what the RAW of that spell would dictate that nobody is shocked that the 60 day limit doesn't apply either.

This idea can be combined with the "one correct item plus many different-looking dummies" idea above.

Another part of the answer:

A room with lots and lots and lots of Glyphs of Warding. Dispelling them one by one would be slow and tedious. Dispelling them in large batches is hard because they're cast on different objects. And while "move the objects via telekinesis until the glyph breaks" can basically work, the room is small enough -- and the spell may be skewed enough -- that the simplest forms of that strategy don't suffice.

On the other hand, Stone Shape could create an outlet for disposing of the booby-trapped items more safely ...

... and come to think of it:

Yet another part of the answer:

Embed access in a wall in a way that makes it only accessible via Stone Shape or else harsh and risky demolition.

[Xervous]

On site: dummy heart in collection system. Drain funnel has a set of ring gates leading to the actual heart. Everyone believes that the heart is enchanted to only produce so much valid blood each day and only when the correct blessing is spoken.