Worlds Missing After Paper 26.x Update? The Dimensions Folder

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Paper 26.x moves every extra world into world/dimensions. Where Multiverse worlds went, the log lines, the backup to take first and how to go back to 1.21.11.

A Minecraft grass block folder icon

You updated a Paper server from 1.21.11 to 26.3, opened the file manager, and the folders of your extra worlds are gone from the server root. creative, resource, lobby: none of them are where they used to be, and the console talks about a "legacy CraftBukkit import". Your worlds are not deleted. Paper moved them into the main world folder, under dimensions. Here is where they went, how Multiverse finds them, and what to do before and after the update.

Quick answer: Worlds missing after a Paper update from 1.21.11 to 26.1 or newer are in the dimensions folder of your main world: world/dimensions/minecraft/<name>/ with the default level-name=world. Paper moves every extra world there the first time it loads, logs "Starting legacy CraftBukkit import for world ...", and then deletes the old folder. The Paper team closed the report about this, issue #14450, as "works as intended": this is how Paper stores worlds since 26.1, and there is no switch to turn it off. Take a full backup first, update Multiverse to 5.8.2 before you update Paper, leave the moved folders where they are, and restore that backup if you need 1.21.11 back.

Where your worlds went: the dimensions folder

Since its 26.1 builds, Paper stores worlds the way vanilla does: as dimensions inside one world folder. The PaperMC 26.1 post shows the new tree for the Overworld, Nether and End. Extra worlds land in the same place. For a server with level-name=world and Multiverse worlds called creative and resource, the server looks like this after the update:

world/
  level.dat
  players/
  dimensions/
    minecraft/
      overworld/
      the_nether/
      the_end/
      creative/
        data/
        entities/
        poi/
        region/
        paper-world.yml
      resource/

The general pattern is <world container>/<level-name>/dimensions/<namespace>/<key>/:

  • level-name comes from server.properties and defaults to world.
  • world container is the folder that holds your world folders. By default that is the server folder itself; world-container in bukkit.yml or the --world-container start flag changes it (Paper docs). That is why the GitHub report shows worlds/default_world/dimensions/minecraft/map: that server keeps its worlds in a worlds folder and calls its main world default_world.
  • namespace and key are the world's ID. A world that a plugin loads by its plain name, which is how Multiverse loads worlds from before 26.1, gets the minecraft namespace and its name in lowercase with spaces turned into underscores (Paper's WorldCreator). So Creative ends up in dimensions/minecraft/creative. A plugin can also use its own namespace: in the Paper team's test on the issue, a world loaded as worlds:machine_terrain moved to world/dimensions/worlds/machine_terrain.

The world keeps its name. Multiverse's docs say worlds in the minecraft namespace "will retain only the second half of the key as the world name, just like before" (Multiverse docs), so /mv tp creative still works.

What exactly moves, per Paper's migration code: the region, entities and poi folders and paper-world.yml go into the new folder. A Multiverse Nether or End world's DIM-1 or DIM1 folder is merged in too. level.dat is not copied: Paper reads it and stores the world's settings in the new folder's data directory, next to its own files such as level_overrides.dat. Then it deletes the old folder, level.dat included. The main world's world_nether and world_the_end make the same move at startup.

The log lines that show the move

You will see two kinds of output. At startup, if the main world, Nether or End still use the old layout, Paper prints this inside an ALERT banner (source):

World storage migration is required during startup.
If you do not have a backup: interrupt the server now. Use Ctrl+C, your panel kill function, etc.
Continuing in 30 seconds...

That is your last chance to stop without a backup.

Extra worlds get no warning. Paper converts each one when a plugin loads it. Multiverse loads every world with auto-load on, the default, while it starts, so on most Multiverse servers this happens during the same startup. Other plugins may wait until someone teleports into the world, which is what happened in the GitHub report. Per world, the log looks like this (from issue #14450, shortened):

[LegacyCraftBukkitWorldMigration] Starting legacy CraftBukkit import for world 'map' (minecraft:map)
[WorldMigrationSupport] Migrating world directory from worlds/map/region to worlds/default_world/dimensions/minecraft/map/region
[WorldMigrationSupport] Migrating world directory from worlds/map/entities to worlds/default_world/dimensions/minecraft/map/entities
[WorldMigrationSupport] Migrating world directory from worlds/map/poi to worlds/default_world/dimensions/minecraft/map/poi
[WorldMigrationSupport] Migrating Paper world config from worlds/map/paper-world.yml to worlds/default_world/dimensions/minecraft/map/paper-world.yml
Starting upgrade for world "map"
Upgrade done for world "map"
[LegacyCraftBukkitWorldMigration] Completed legacy CraftBukkit import for world 'map' (minecraft:map)

The part in brackets, minecraft:map, is the key, and it names the folder: dimensions/minecraft/map. Search your log for "legacy CraftBukkit import" to list every world that moved.

What the Paper team says

The reporter of #14450, filed on 1 November 2026, asked: "How to stop the worlds from moving into the dimensions folder?" A Paper contributor answered on 2 November that this is how worlds are stored now, because "Mojang changed the folder structure and split up some files in 26.1". The contributor tested the reporter's world on 1.21.11 and on 26.3, saw nothing wrong with it, and closed the issue with the label "works as intended".

Back up before you update

Once a world is migrated, its old folder no longer exists. PaperMC calls backups "absolutely mandatory" for this update and writes that a world upgraded to 26.1 cannot be downgraded. Paper's updating guide lists what to save: the world folders, the server configuration files, and the plugin configs and jars. On a Multiverse server that means:

  • every world folder: world, world_nether, world_the_end and each extra world, or your whole world container folder;
  • plugins/Multiverse-Core/worlds.yml and the rest of plugins/;
  • server.properties, bukkit.yml, spigot.yml and the config folder.

A backup of the whole server folder covers all of it. Download one copy as well, so it lives off the server. On Space-Node Minecraft hosting you make that backup yourself in the panel, and afterwards you can check the new folders in the web-based file manager or over SFTP. Our Pterodactyl restore guide shows how to bring such a backup back.

How Multiverse 5.8.2 finds the moved worlds

Multiverse-Core 5.8.2 came out on 26 October 2026. Its release notes mark the builds as compatible with 26.3 and list "Update legacy world name on world load". Modrinth lists 5.8.2 for every version from 1.18.2 up to 26.3, 1.21.11 included, so you can install it while the server still runs 1.21.11 and update Paper after that. Use that order, because an older Multiverse does not know the new layout: 26.1 support started in 5.6.0 (5 April 2026), and 5.7.0 (7 June 2026) began storing worlds in worlds.yml by namespaced key and showing that key in /mv info (all releases).

On Paper 26.1 or newer, Multiverse first looks for a world in <level-name>/dimensions/<namespace>/<key>. If that folder does not exist yet but the old folder in the server root does, it uses the old one (WorldFolderResolver). That is why the first start after the update works: Multiverse finds creative/ in the old place, asks Paper to load minecraft:creative, and Paper moves it. On the next start Multiverse finds it in the new place. Your worlds.yml entries, aliases and world properties stay as they were.

Three commands to check the result:

/mv list
/mv info creative
/mv load creative

/mv info shows the key, which is the folder path under dimensions. To add an old world from another server, one with level.dat inside, upload the folder to the server root as before and import it with its environment:

/mv import arena normal

Paper moves it to world/dimensions/minecraft/arena while it loads. For a world that already sits in the dimensions folder, Multiverse's import docs say to pass the namespaced key instead, such as minecraft:arena. The addons have 26.3 builds too: on Modrinth, Multiverse-Portals 5.3.0, Multiverse-Inventories 5.3.6 and Multiverse-NetherPortals 5.1.0 all list 26.3.

Update a Multiverse server from 1.21.11 to 26.3, step by step

  1. Make the full backup from the previous section and download a copy.
  2. Still on 1.21.11, update Multiverse-Core to 5.8.2 and the addons you use. Restart once and check /mv list.
  3. If you can, run the update on a copy first. Our test server guide shows how.
  4. Stop the server, switch to Paper 26.3 and set Java 25, which Paper lists as the minimum for 26.3. On 3 November 2026 the newest build is 238, from 2 November.
  5. Start the server and watch the console: the ALERT banner, the startup migration, then one "legacy CraftBukkit import" block for every Multiverse world.
  6. Run /mv list and /mv info for each world, teleport in, and check a few builds you know.
  7. Fix everything that uses the old folder paths (next section).
  8. Keep the pre-update backup until the server has run for a while with players on it.

Everything else that changes with 26.3, from plugins to the whitelist default, is in our 26.3 server update guide.

Plugins, scripts and tools that use world paths

Plugins that address worlds by name through the server API keep working, because the name does not change. What breaks is anything that works with folders directly:

  • Backup scripts and cron jobs that copy creative/ or world_nether/ find nothing. Everything now sits inside world/, so one copy of that folder holds all worlds, and it is bigger than before.
  • .pteroignore lines that skip a world folder in panel backups, such as resource/, match nothing now. Use the new path, world/dimensions/minecraft/resource/.
  • Reset scripts that delete a resource world's folder by name stop working. Reset through Multiverse instead: /mv regen resource regenerates the world with the same seed, or with a new one if you add --seed.
  • BlueMap map configs in plugins/BlueMap/maps/ have a world: line with a folder path and a dimension: line with a key. On Paper 26.x, BlueMap's Paper build uses the main world folder for every world and the world's key as the dimension (source), so the map of creative needs world: pointing at world and dimension: "minecraft:creative". BlueMap 5.19 fixed wrong world paths in its default configs on new Paper builds, and 5.24 added 26.3 worlds.
  • Tools that open a downloaded copy, such as map editors or region tools, need the new path: the region files of creative are in world/dimensions/minecraft/creative/region/.
  • Plugin developers: the 26.1 post marks WorldInfo#getName as obsolete and asks for getKey instead.

Do not move the folders back out

The reporter on GitHub took the worlds out of the dimensions folder again, put back a level.dat from a backup, and found every world empty in game. Leave the folders where the migration put them, and if you already moved them, restore your backup instead of moving folders by hand.

Paper finds a world by its key. Load map under another key, say myplugin:map, and Paper finds no data in dimensions/myplugin/map and generates a new world there (CraftServer source). If a world comes up as fresh terrain after the update, compare its key in /mv info with the folder names under dimensions before you change anything.

How to go back to 1.21.11

A migrated world does not go back. PaperMC says you cannot downgrade after upgrading to 26.1, and Paper's migration page only describes moving files from Paper 26.1 or newer to vanilla, not to an older version. Going back means restoring the backup:

  1. Stop the server.
  2. Restore the full backup from before the update, so the jar, plugins, configs and worlds all come from the same moment. In Pterodactyl, tick "Delete all files before restoring backup." so the new dimensions tree is removed as well.
  3. Set the server version back to Paper 1.21.11, which needs Java 21 or newer.
  4. Start it and check /mv list.

Don't plan to stay there: Paper's download service marks 1.21.11 as unsupported since 15 June 2026, and its last build, 132, came out on 11 May 2026. A rollback buys time to fix a script or a plugin, nothing more.

FAQ

How do I stop the worlds from moving into the dimensions folder?

You can't on Paper 26.1 or newer. The Paper team closed issue #14450 as "works as intended": every world is a dimension of the main world now, because Mojang changed the folder structure in 26.1. The only way to keep the old layout is to stay on 1.21.11, which Paper no longer supports.

Where are my Multiverse worlds after updating Paper?

In <level-name>/dimensions/minecraft/<name>/, so world/dimensions/minecraft/creative/ with the default level-name=world. If you use a world container, that folder comes first. /mv info <world> shows the key, and the key is the path under dimensions.

Why are world_nether and world_the_end gone?

Paper moved them at startup to world/dimensions/minecraft/the_nether and world/dimensions/minecraft/the_end. Only the folders changed.

Can I move the worlds back out of the dimensions folder?

No. The reporter of #14450 who did that found empty worlds. If you moved them already, restore your backup.

Do I have to import my worlds in Multiverse again?

No, if Multiverse already knew them. Multiverse 5.7 and newer stores worlds by key and checks both the new and the old location, so worlds in worlds.yml load and get migrated by themselves. Update to 5.8.2 before you update Paper.

Can I downgrade from 26.3 to 1.21.11 after the migration?

Not with the migrated worlds. Restore the full backup you made before the update.

Sources

All opened on 3 November 2026: