In WoW SoD Phase 4 (and of course in vanilla WoW too), Upper Blackrock Spire is one of several dungeons that become available at max level, and a great place to farm gear, at max level. But to get into Upper Blackrock Spire, you must complete the UBRS Attunement quest chain, which allows you to unlock the door to the second half of the sprawling Blackrock Spire dungeon.