diff --git a/paper-api/src/main/java/org/bukkit/WorldCreator.java b/paper-api/src/main/java/org/bukkit/WorldCreator.java
index 6fb3c2fa739f..1e6a84b4cdd1 100644
--- a/paper-api/src/main/java/org/bukkit/WorldCreator.java
+++ b/paper-api/src/main/java/org/bukkit/WorldCreator.java
@@ -3,6 +3,7 @@
 import com.google.common.base.Preconditions;
 import java.util.Random;
 import io.papermc.paper.math.Position;
+import net.kyori.adventure.key.Key;
 import org.bukkit.command.CommandSender;
 import org.bukkit.generator.BiomeProvider;
 import org.bukkit.generator.ChunkGenerator;
@@ -15,13 +16,14 @@
  * Represents various types of options that may be used to create a world.
  */
 public class WorldCreator {
-    private final NamespacedKey key; // Paper
+    private final NamespacedKey key;
     private final String name;
     private long seed;
     private World.Environment environment = World.Environment.NORMAL;
     private ChunkGenerator generator = null;
     private BiomeProvider biomeProvider = null;
     private WorldType type = WorldType.NORMAL;
+    private @Nullable Key customEnvironmentKey = null;
     private boolean generateStructures = true;
     private String generatorSettings = "";
     private boolean hardcore = false;
@@ -151,6 +153,9 @@ public WorldCreator copy(@NotNull World world) {
 
         seed = world.getSeed();
         environment = world.getEnvironment();
+        if (environment == World.Environment.CUSTOM) {
+            customEnvironmentKey = world.getEnvironmentKey();
+        }
         generator = world.getGenerator();
         biomeProvider = world.getBiomeProvider();
         type = world.getWorldType();
@@ -173,6 +178,7 @@ public WorldCreator copy(@NotNull WorldCreator creator) {
 
         seed = creator.seed();
         environment = creator.environment();
+        customEnvironmentKey = creator.customEnvironmentKey();
         generator = creator.generator();
         biomeProvider = creator.biomeProvider();
         type = creator.type();
@@ -231,15 +237,49 @@ public World.Environment environment() {
     }
 
     /**
-     * Sets the environment that will be used to create or load the world
+     * Sets the environment that will be used to create or load the world.
+     * <p>
+     * <b>Note:</b> if the environment is {@link World.Environment#CUSTOM},
+     * then you also need to set the key using {@link #customEnvironmentKey(Key)}.
      *
      * @param env World environment
      * @return This object, for chaining
+     * @see #customEnvironmentKey(Key)
      */
     @NotNull
     public WorldCreator environment(@NotNull World.Environment env) {
         this.environment = env;
 
+        if (env != World.Environment.CUSTOM) {
+            this.customEnvironmentKey = null;
+        }
+
+        return this;
+    }
+
+    /**
+     * Gets the environment key that will be used to create or load the world
+     * if {@link #environment()} is {@link World.Environment#CUSTOM}.
+     *
+     * @return World environment key
+     */
+    @ApiStatus.Experimental
+    public @Nullable Key customEnvironmentKey() {
+        return customEnvironmentKey;
+    }
+
+    /**
+     * Sets the environment key that will be used to create or load the world and
+     * set the environment to {@link World.Environment#CUSTOM}.
+     *
+     * @param customEnvironmentKey World environment key
+     * @return This object, for chaining
+     */
+    @ApiStatus.Experimental
+    public @NotNull WorldCreator customEnvironmentKey(@NotNull Key customEnvironmentKey) {
+        this.environment = World.Environment.CUSTOM;
+        this.customEnvironmentKey = customEnvironmentKey;
+
         return this;
     }
 
diff --git a/paper-api/src/main/java/org/bukkit/generator/WorldInfo.java b/paper-api/src/main/java/org/bukkit/generator/WorldInfo.java
index 6c8d4f817f4f..d8ea2a824313 100644
--- a/paper-api/src/main/java/org/bukkit/generator/WorldInfo.java
+++ b/paper-api/src/main/java/org/bukkit/generator/WorldInfo.java
@@ -2,6 +2,7 @@
 
 import java.util.UUID;
 import io.papermc.paper.world.flag.FeatureFlagSetHolder;
+import net.kyori.adventure.key.Key;
 import org.bukkit.Keyed;
 import org.bukkit.World;
 import org.jetbrains.annotations.ApiStatus;
@@ -40,6 +41,14 @@ public interface WorldInfo extends FeatureFlagSetHolder, Keyed {
     @NotNull
     World.Environment getEnvironment();
 
+    /**
+     * Gets the environment key for this world.
+     *
+     * @return This world Environment key
+     */
+    @ApiStatus.Experimental
+    @NotNull Key getEnvironmentKey();
+
     /**
      * Gets the Seed for this world.
      *
diff --git a/paper-server/patches/sources/net/minecraft/server/MinecraftServer.java.patch b/paper-server/patches/sources/net/minecraft/server/MinecraftServer.java.patch
index 595172fa7bfd..bc557943d767 100644
--- a/paper-server/patches/sources/net/minecraft/server/MinecraftServer.java.patch
+++ b/paper-server/patches/sources/net/minecraft/server/MinecraftServer.java.patch
@@ -274,7 +274,7 @@
          if (profiledDuration != null) {
              profiledDuration.finish(true);
          }
-@@ -415,33 +_,150 @@
+@@ -415,33 +_,151 @@
          }
      }
  
@@ -343,6 +343,7 @@
 +            worldDataAndGenSettings.genSettings().options().seed(),
 +            worldDataAndGenSettings.data().enabledFeatures(),
 +            loading.info().environment(),
++            io.papermc.paper.adventure.PaperAdventure.asAdventureKey(loading.info().stemKey()),
 +            levelStem.type().value(),
 +            levelStem.generator(),
 +            this.registryAccess(),
diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java b/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java
index 83b8d44c7c8f..03e1c754d587 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/CraftServer.java
@@ -10,6 +10,7 @@
 import com.mojang.brigadier.StringReader;
 import com.mojang.brigadier.exceptions.CommandSyntaxException;
 import com.mojang.serialization.JsonOps;
+import io.papermc.paper.adventure.PaperAdventure;
 import io.papermc.paper.configuration.GlobalConfiguration;
 import io.papermc.paper.configuration.PaperServerConfiguration;
 import io.papermc.paper.configuration.ServerConfiguration;
@@ -1168,6 +1169,9 @@ public World createWorld(WorldCreator creator) {
         Preconditions.checkState(this.console.getAllLevels().iterator().hasNext(), "Cannot create additional worlds on STARTUP");
         //Preconditions.checkState(!this.console.isIteratingOverLevels, "Cannot create a world while worlds are being ticked"); // Paper - Cat - Temp disable. We'll see how this goes.
         Preconditions.checkArgument(creator != null, "WorldCreator cannot be null");
+        if ((creator.environment() == Environment.CUSTOM) == (creator.customEnvironmentKey() == null)) {
+            throw new IllegalArgumentException("Custom environment key cannot be null when environment is CUSTOM and vice versa");
+        }
 
         String name = creator.name();
         ChunkGenerator chunkGenerator = creator.generator();
@@ -1194,7 +1198,7 @@ public World createWorld(WorldCreator creator) {
             case NORMAL -> LevelStem.OVERWORLD;
             case NETHER -> LevelStem.NETHER;
             case THE_END -> LevelStem.END;
-            default -> throw new IllegalArgumentException("Illegal dimension (" + creator.environment() + ")");
+            case CUSTOM -> PaperAdventure.asVanilla(Registries.LEVEL_STEM, creator.customEnvironmentKey());
         };
 
         RegistryAccess registryAccess = this.console.registryAccess();
@@ -1271,7 +1275,7 @@ public World createWorld(WorldCreator creator) {
             throw new IllegalStateException("Missing level stem for world " + name + " using key " + actualDimension);
         }
 
-        WorldInfo worldInfo = new CraftWorldInfo(loadedWorldData.bukkitName(), CraftNamespacedKey.fromMinecraft(dimensionKey.identifier()), genSettingsFinal.options().seed(), primaryLevelData.enabledFeatures(), creator.environment(), customStem.type().value(), customStem.generator(), registryAccess, loadedWorldData.uuid());
+        WorldInfo worldInfo = new CraftWorldInfo(loadedWorldData.bukkitName(), CraftNamespacedKey.fromMinecraft(dimensionKey.identifier()), genSettingsFinal.options().seed(), primaryLevelData.enabledFeatures(), creator.environment(), io.papermc.paper.adventure.PaperAdventure.asAdventureKey(actualDimension), customStem.type().value(), customStem.generator(), this.getHandle().getServer().registryAccess(), loadedWorldData.uuid());
         if (biomeProvider == null && chunkGenerator != null) {
             biomeProvider = chunkGenerator.getDefaultBiomeProvider(worldInfo);
         }
diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/CraftWorld.java b/paper-server/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
index f3f068011abd..699bcfb2122c 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/CraftWorld.java
@@ -7,6 +7,7 @@
 import com.google.common.collect.Lists;
 import com.mojang.datafixers.util.Pair;
 import io.papermc.paper.FeatureHooks;
+import io.papermc.paper.adventure.PaperAdventure;
 import io.papermc.paper.entity.poi.PaperPoiSearchResult;
 import io.papermc.paper.entity.poi.PaperPoiType;
 import io.papermc.paper.entity.poi.PoiSearchResult;
@@ -34,6 +35,7 @@
 import java.util.function.Consumer;
 import java.util.function.Predicate;
 import java.util.stream.Collectors;
+import net.kyori.adventure.key.Key;
 import net.kyori.adventure.pointer.PointersSupplier;
 import net.minecraft.SharedConstants;
 import net.minecraft.core.BlockPos;
@@ -874,6 +876,11 @@ public boolean createExplosion(Location loc, float power, boolean setFire, boole
         return this.environment;
     }
 
+    @Override
+    public @NotNull Key getEnvironmentKey() {
+        return PaperAdventure.asAdventureKey(this.getHandle().getTypeKey());
+    }
+
     @Override
     public @Nullable ChunkGenerator getGenerator() {
         return this.world.generator;
diff --git a/paper-server/src/main/java/org/bukkit/craftbukkit/generator/CraftWorldInfo.java b/paper-server/src/main/java/org/bukkit/craftbukkit/generator/CraftWorldInfo.java
index f92a9daafb05..312d15727d5e 100644
--- a/paper-server/src/main/java/org/bukkit/craftbukkit/generator/CraftWorldInfo.java
+++ b/paper-server/src/main/java/org/bukkit/craftbukkit/generator/CraftWorldInfo.java
@@ -1,6 +1,7 @@
 package org.bukkit.craftbukkit.generator;
 
 import java.util.UUID;
+import net.kyori.adventure.key.Key;
 import net.minecraft.core.RegistryAccess;
 import net.minecraft.world.flag.FeatureFlagSet;
 import net.minecraft.world.level.chunk.ChunkGenerator;
@@ -17,6 +18,7 @@ public class CraftWorldInfo implements WorldInfo {
     private final NamespacedKey dimension;
     private final UUID uuid;
     private final World.Environment environment;
+    private final Key environmentKey;
     private final long seed;
     private final int minHeight;
     private final int maxHeight;
@@ -30,6 +32,7 @@ public CraftWorldInfo(
         long seed,
         FeatureFlagSet enabledFeatures,
         World.Environment environment,
+        Key environmentKey,
         DimensionType dimensionType,
         ChunkGenerator vanillaChunkGenerator,
         RegistryAccess registryAccess,
@@ -40,6 +43,7 @@ public CraftWorldInfo(
         this.seed = seed;
         this.enabledFeatures = enabledFeatures;
         this.environment = environment;
+        this.environmentKey = environmentKey;
         this.minHeight = dimensionType.minY();
         this.maxHeight = dimensionType.minY() + dimensionType.height();
         this.vanillaChunkGenerator = vanillaChunkGenerator;
@@ -67,6 +71,11 @@ public long getSeed() {
         return this.seed;
     }
 
+    @Override
+    public Key getEnvironmentKey() {
+        return this.environmentKey;
+    }
+
     @Override
     public int getMinHeight() {
         return this.minHeight;