The 
Planarium is a block from Ars Nouveau that holds its own little pocket dimension, which you’re able to step inside and build in. Anything you build in there shows up as a tiny model inside the jar, so it’s a bit like having a ship in a bottle that you can walk around in, and it’s only in the 1.21.1 version of the mod.
People usually use it as a private room, a storage area or a small farm that doesn’t take up any space in their actual base. It’s made in the 
Enchanting Apparatus from a 
Containment Jar, and it needs a name before it’ll create a dimension to go into.
Crafting the Planarium
To make a Planarium, put a Containment Jar in the middle of the Enchanting Apparatus with a 
Stabilized Warp Scroll, a 
Conjuration Essence and a 
Diamond on the Arcane Pedestals around it. The recipe doesn’t use any Source, although the Stabilized Warp Scroll takes a bit of work to make first.
The Planarium is two blocks tall, so it needs an empty space above wherever you place it. Using it while it doesn’t have a name yet just tells you to name it, as that’s what decides which dimension it opens.
Naming and Entering the Planarium
You’re able to name a Planarium by renaming it in an 
Anvil before placing it, or by casting a spell with the 
Name glyph on it. Once it has a name, it creates a pocket dimension with that name, and sneaking and using the Planarium sends you inside.
Every Planarium with the same name opens the same dimension, so two jars with the same name in different parts of your world both lead to the same room. Leaving always sends you back to the jar you went in through though, so it works as a shared room rather than a shortcut between them.
Inside the Pocket Dimension
The space inside is a box of about 30 blocks in each direction, closed in by walls on every side. It’s always night in there and there’s no sky light, so you’ll want to bring 
Torches or Magelights with you to light it up, and beds do still work if you’d like to set your spawn inside.
To leave, just break any of the walls of the dimension, which sends you back to where you came in. You’re also able to set where you appear when you enter, by using the 
Dominion Wand on one of the walls and then on the spot you’d like to spawn.
Frequently Asked Questions
Name the Planarium in an Anvil or with the Name glyph, then sneak and use it. The name decides which pocket dimension it opens.
Break any of the walls of the dimension, and you’ll be sent back to where you entered from.
No, the Planarium was added in the 1.21.1 version of Ars Nouveau and isn’t in 1.20.1.
Yes, every Planarium with the same name opens the same pocket dimension, although you always leave back through the jar you entered from.
