The Hidden Secret

The only way to enter this level is by first opening any campaign or sandbox level. From there, you must use the search function in the parts library and enter this phrase:

It must be written exactly that way, with no capitals. Doing this in the level editor will result in nothing. This level can be accessed from the DLC as well. You and your machine will be taken to a new hellish looking landscape.

After this point is where the spoilers come! I suggest not reading any further if you want to leave the discovery to yourself!

When you and your machine arrive, the bounding box will start off DISABLED. There is no clear objective or instruction, but there might be a way to conquer this stage as it's still possible to make progress. This level also lacks an introduction title like all the others have, meaning it might not have an official name.

It's a little bit dark in this place, except for the light shining from your machine. This level also has elements from every other base-game island.

The blue flaming torches cannot be extinguished, nor can they ignite anything.

On the opposite side of your machine, there's a massive bowl surrounded by tiles on the floor. Each tile represents a level in the vanilla campaign, and will light up blue if you've beaten a level. I've tried sacrificing a plane into the bowl and burning it. This didn't accomplish anything.

There are massive dragon bones laying about the outskirts of the scene. I've scouted all of them and there seems to be nothing of note around them.

There are strange Ipsilon knights standing around. They are quite durable and are harder than usual to kill. They can't be set on fire and will also survive a direct impact against a bomb.

When close enough, they will hurl blue fireballs at your machine. These fireballs not only ignite wooden parts, but also deal damage on impact so protecting yourself with water cannons won't save you. Their fireballs also bounce around for a bit.

If you've turned the machine bounding box back on and disabled god powers, killing the knights will give points towards level progress. But even if you defeat them all, you will only have just over 50% completed the stage. It's possible for a knight get knocked into inside one of the rocks, making it impossible to kill them if this happens.

Each knight is special and has their own unique name. They each represent somebody who worked on the game. Instead of a cause of death, the role they played in the creation of Besiege is displayed. Most of them seem to be Artists. They also leave no corpses on death, instead vanishing in a puff of blue flames.

As of the 'Major Level Editor Update' These guys can now be used in custom levels. The official name for this enemy type has been revealed as "Besiege Developer". According to the level editor, they have a whopping 2000 health (Over twice the hitpoints of the base games strongest NPCs)! They are innately hostile towards to all other life forms (including animals) except for peasants, fishermen, and other Besiege Developers.

I don't know if there's a way to beat it. Defeating the knights gives progress, but it's only one half of this puzzle as they only provide just over 50%. I couldn't find any other way to make progress.

Update: Killing almost all of the knights and then bringing your source cube to the bowl will cause an event where it floats into the bowl and ignites a massive blue bonfire. Your source cube must be loose and not connected to anything (Preferably held in a holder) for the event to happen. Only 50% progress must be made, meaning one knight can be left alive if you can call that "mercy". Strangely, this scene this doesn't grant additional progress. It's best to assume your ring must be fully lit up (All levels conquered) first for this to happen as well.

All tests were done with level progression enabled!

• Progress can only be made when cheats are off (Bounding box enabled and no god powers).
  
• Killing all the knights gives just over 50% progress. Even trying it with all levels beaten doesn't change this.
  
• The blue fire pillars don't burn your vehicle (Including the hottest one).
  
• The blue fire pillars can't be extinguished by a water cannon (Also including the hottest one).
  
• The only things that can be destroyed are the knights and the tombstones.
  
• Destroying the tombstones awards no progress.
  
• The small floating stones can be crashed into if you fly into them.
  
• The chains don't have collision and seem to do nothing.
  
• There's nothing interesting around the dragon skeletons.
  
• Burning your machine inside the huge bowl does nothing.
  
• Searching 'the hidden secret' again while inside this stage does nothing.
  
• Searching 'the hidden answer' had no results.
  
• Being struck by lightning has no unusual effects.
  
• At 50% progress, your starting block (If unattached to anything) will float into the bowl when brought into the ring. It's best to assume all levels must have been conquered for this to happen. Oddly, this spectacle still doesn't grant any progress.
  
• Having the Supporter or Achievement Cube skin enabled for the starting block doesn't appear to have any different effects. (By extension, having 100% completion grants nothing neither).

I couldn't find a purpose for most of these things but hopefully these observations lead to something in the future. The sentences in bold are clues I think are the most important.

• The massive bowl looks identical to the one used to melt gold in Krolmar (zone 47).
  
• The bowl can hold things.
  
• The ring of tiles surrounding the huge bowl each signify a campaign level in the base game and whether they've been beaten or not.
  
• Middle-mouse-clicking the bowl brings your camera underneath the map below it. It could be an invisible object linked to the bowl.
  
• When a knight perishes, they leave a blue spirit behind for just a second. Maybe something can be done with this?
  
• The knights are wearing red. It's possible this whole thing could just be a massive, expensive red-herring.
  
• The knights clothing is the same shade of red as the candles.
  
• The knights are wearing Ipsilon helmets.
  
• Each knight represents somebody who helped make Besiege.
  
• Your machine emits light in this stage.
  
• A lyre statue (zone 11), a giants sword (zone 30), several dragon skeletons (zone 42), and a fruitless Tree of Akhmora (zone 49) can also be spotted in this level.
  
• If the search tool gets you here, maybe there's another phrase that does something else...
  
• One of the pillars is burning hotter than the rest, with actual blue flames blazing violently. You can see it easy if you zoom out and spot the smoke coming from it.

I wrote this "guide" in an attempt to raise more awareness about The Hidden Secret since I couldn't find very much info about it. Yeah, I know it's meant to be a "hidden secret" but it's still content in the game that we all paid for, and it's pretty damn huge for a secret.

Hopefully my writings here can help someone beat the level, seeing as I can't find a way to do it at the moment. It's also important to remember that this secret might not mean anything at all and could be designed to be an impossible puzzle.