The Collapsed Kingdom is sealed in two places, and the Somber Key is the only thing that gets you past either of them. It’s a key that also works as a sword, made by joining two halves that the armored minibosses inside the kingdom carry.
You’ll meet the lock long before you hold the key. In the kingdom’s tower you’ll walk out onto a wide stone hatch set into the floor, and a message will appear in your hotbar telling you to right-click the trapdoor with a Somber Key. The hatch itself can’t be mined, and the shaft underneath it is cased in 
Indestructible Block, so there’s no digging around the problem.
Obtaining
Both halves come off minibosses, one each, and neither of them is a chance roll. The Beheaded Knight carries the 
Somber Key Blade and the Resurrected Knight carries the 
Somber Key Ring, so you’ll need to kill one of each to hold a complete key. Both also leave 
Metal Debris behind when they go down.
| Miniboss | Health | Guaranteed Drops |
|---|---|---|
| Beheaded Knight | 195 | Somber Key Blade, Metal Debris |
| Resurrected Knight | 190 | Somber Key Ring, Metal Debris |
The pair is always placed asleep, and while they’re down like that they can’t be hurt at all, so nothing you throw at them registers. Coming within about 10 blocks wakes them, and they take a couple of seconds to stand up, so the window is for getting into position rather than free hits. Neither takes knockback, so you can’t shove them back off you once the fight starts.
Neither knight spawns out in the world on its own, they’re only ever placed inside The Collapsed Kingdom. A structure generates two of each, which works out at exactly two Somber Keys per kingdom, and there are exactly two hatches waiting to take them.
The kingdom itself sits under Plains, Forest, Birch Forest and Old Growth Birch Forest, and the command points you at its gatehouse on the surface. The first pair of knights is in the tower behind that gatehouse, in the same room as the first hatch.
Once you have both halves, the craft is shapeless, so your inventory grid will do it and you won’t need to find a 
Crafting Table first. The halves are worth nothing on their own, as the only thing either of them does is make the key.
Keep the key in your hotbar once it’s made, because the first hatch is in the same room as the knights that dropped the halves. There’s nothing else to prepare between the craft and the door.
Usage
The Two Locked Hatches
A 
Somber Trapdoor is a three by three slab of floor, and only the center block takes the key. Right clicking anywhere else does nothing, and the hotbar message that keeps appearing doesn’t tell you that, so aim for the middle block. Each hatch takes one key and the key is consumed, though it stays open permanently afterward, so you only ever pay once per door.
The Ruins Hatch
Opens the route down into the pits
The first hatch is set into the floor of the tower with a Beheaded Knight and a Resurrected Knight asleep in the same room, which is a fairly heavy hint about what it takes to open it. Underneath is the pit shaft, and that chain of pits is the only way to reach the dungeon level at all.
The Arena Hatch
The last door before the boss
Deep in the dungeon a second hatch sits at the end of a room with its own pair of knights asleep in front of the door they lock. This one drops straight into the Possessed Paladin‘s arena, and every other branch of the dungeon dead ends, so there’s no route to the boss that avoids it.
The hatch opens a moment after the key goes in and the collision disappears with it, so whatever you were standing on is gone. Both shafts are long enough to kill you from full health, and neither has 
Ladders or Water in it.
Bring a way down before you use a key. Both hatches open onto a bare shaft, and both drops are long enough to kill you outright at full health, so keep a 
Water Bucket or a 
Potion of Slow Falling in the hotbar when you right-click the lock.
Using It As A Weapon
The Somber Key is registered as a sword, so it swings like one and takes the normal sword enchantments. It hits for 7.5 at an attack speed of 1.5, which is slightly harder and slightly slower than a 
Diamond Sword.
Somber Key
Diamond Sword
Netherite Sword
Durability is where it falls behind, as 350 swings won’t last long in a structure this size. 
Gold Ingots repair it on an 
Anvil cheaply enough, though Mending is the better answer if you’re planning to carry it, and it takes enchantments about as readily as an 
Iron Sword does.
The real cost isn’t durability, it’s the door. Every swing you take with a Somber Key is a key you’re not spending on a hatch, and a kingdom only ever gives you two of them.
Tips
Get decent armor on before you go looking for the first hatch, as the knight pair guarding it chews through a full set fast even when you’re geared up well. The Beheaded Knight swings for 15 to 18 and the Resurrected Knight for 13 to 15, and blocking won’t save you either, since a hit on a raised 
Shield puts it on cooldown for 5 seconds.
Split the two knights guarding a hatch if the room lets you, as they only link up while they’re within about 10 blocks of each other. Pulling one of them back down a corridor past that range breaks the pairing, and you’ll be able to take them one at a time instead of facing the attacks they throw together.
Clear the room and set up before you walk into wake range, since nothing lands on a sleeping knight anyway. They need a couple of seconds to get up once you’ve triggered them, which is enough time to drink something or back into a doorway where only one of them can reach you.
Hold on to the Metal Debris that drops alongside the halves, as 2 of them with 2 
Iron Nuggets and a 
Stick makes a 
Shattered Greatsword. Four knights across the kingdom means enough debris for two weapons, and that’s a reasonable thing to be crafting on the way to the arena anyway.
If you do want to keep one as a sword, plan for a second structure. Kingdoms are spread about 110 chunks apart, so it might be a long trip, and until you’ve spent a key on the arena hatch the Possessed Paladin stays out of reach.
FAQ
Every Collapsed Kingdom generates two locked hatches, one in the ruins and one in front of the arena, and each takes a key that’s used up on the spot. The structure also places two Beheaded Knights and two Resurrected Knights, so a full clear gives you exactly the two keys it asks for, with nothing spare.
The hatch is built on 
Bedrock‘s properties, so no tool in survival will touch it and explosions won’t either. Tunneling past it doesn’t work as a plan, as the shaft it covers is lined with Indestructible Block on every side, which leaves the key as the only way through.
Both halves only come from the minibosses, as neither appears in the kingdom’s basic or luxury 
Chest loot. The Beheaded Knight always drops the Blade and the Resurrected Knight always drops the Ring, so a Chest run won’t get you anywhere, you’ll have to fight both of them.
They’re placed asleep and take no damage at all in that state, so 
Arrows and melee hits both pass straight through. Walking within about 10 blocks wakes them, and they’ll stand up over a couple of seconds before they can be hurt or can hurt you back.
