Players need to be level 80 and find the entrance to Blackrock Caverns in order to use the Dungeon Finder for the instance, but only need to be level 77 and own Cataclysm to enter Blackrock Caverns via the instance portal. The entrance is just off of the main ring in Blackrock Mountain on the non-jumping path to Blackrock Spire. Head to the eastern side of the ring to see the summoning stone for Blackrock Spire and follow the path. As it turns north there is a blockade blocking the way. Look right to see the instance line.