Its a brand new sub section in EPL. I saw a leak of DK creation at blizzcon showing you start high in the sky on some sort of buildng, so i kept searching around the plaguelands till i matched the skybox and texture for the ground (Which turned out to be a citadel).
The area is basicly a floating citadel, underneath it is a tower and a bit to the south is a new addition to Tyr's Hand.
The Scarlet flags have been ripped down and replaced with a new flag for DKs (Looks like the scourge logo from Wc3).
If you dont want to worldport, the area is just east of Light's Hope.
Speculation: There is probably a begining quest guy on the top who will teleport you to the inside of the citadel, where you can use the portal down. I would also guess the tower is the main quest hub where you can go to attack Tyr's Hand or the Noxious Glades.