Because this add-on is a data pack built for the Deeper and Darker mod, it operates per world save rather than loading globally across every world automatically. Before traveling into the Otherside dimension, confirm that the pack is active in your current save so the new underground structures can generate.
Activating in a New or Existing Save
When creating a fresh world, open the Data Packs menu on the world creation screen and move the pack into the Selected column before generating the world. If you want to add the dungeons to an existing save, open your world folder, place the pack inside the datapacks directory, and run /reload once you load in. Keep in mind that the 2 massive dungeon layouts will only appear in newly explored chunks of the Otherside dimension.
Checking Pack Status
To make sure the game recognizes the pack alongside the Deeper and Darker mod, open the chat window and run /datapack list. Check the enabled list to confirm the pack is active without errors. Once verified, travel to unexplored underground sections of the Otherside to encounter the new dungeon layouts.