Subspace Bubble

Subspace Bubble is a challenge advancement in the Nether tab of Minecraft's advancement system, carrying the in-game description "Use the Nether to travel 7 km in the Overworld." It branches directly off Nether, so that earlier advancement is its prerequisite and must be earned first. The Nether tab covers advancements for exploring and conquering the Nether dimension, from entering the portal to brewing potions. Subspace Bubble was added in Minecraft 1.12 and is still in the 26.2 advancement set.

It is rated Hard difficulty on this site: requires significant effort, rare resources, or dangerous encounters. Because it is flagged as a challenge advancement, completing Subspace Bubble makes a special toast and a sound play, and its frame in the advancement screen is the magenta challenge style rather than a normal square. Challenges are the hardest tier and usually represent a milestone rather than routine progress. Nothing else in the tree depends on it, so it is a leaf at the tip of its branch.

In tree terms, Subspace Bubble sits first along its line: the full path from the Nether root reads Nether -> Subspace Bubble. That means 1 advancement must be completed before this one becomes available, and Subspace Bubble is one of 23 total advancements in the Nether tab. It shares its parent with 7 sibling advancements (Return to Sender, Those Were the Days, Hidden in the Depths, A Terrible Fortress, Who is Cutting Onions?, Oh Shiny, and This Boat Has Legs), all of which open from the same point in the tree.

Completing Subspace Bubble grants 100 experience points, reflecting its status as a challenge, and challenge advancements pay out far more XP than ordinary tasks. The XP drops at your position the moment the advancement fires.

It is a leaf advancement, so nothing further unlocks from it; it stands as a completed tip of its branch.