Was it destroyed during the Cabal invasion? Doesn’t look like it from the crucible map with it in the background.
Lore wise, why can’t we visit it?
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The same reason you can't go to the moon, old russia, mars, venus, the dreadnaught, the reef, etc. Those areas were a part of the D1 map and storyline, and not a part of the D2 storyline. It's the same reason you can't go to the imperial city in skyrim, to Eden prime in mass effect 2, to denerim in Dragon age 2, to Rome in assasins creed 3, etc. The area was not created for the sequel.