IGN has posted a designer diary for the upcoming expansion, Eye of the North. The diary outlines the basic story and how things have changed in Ascalon:
The Depths
The Dwarves have provided limited information about the mysteries they have uncovered beneath the earth. Initial reports describe an immense, interconnected, underground complex the Dwarves call 'the Depths of Tyria'. The Depths are a combination of natural caves and excavations by the Dwarves and other subterranean races housing structures left behind by previous civilizations that date back to a time before the arrival of humans in Tyria.
The Depths are connected by a series of magical gateways that allow swift travel through miles of earth and stone. These gateways were created by creatures known as the Asura. Little is known of this race as its members have not been spotted on the surface in ages, but legends suggest that they are diminutive creatures with large eyes and long ears. The Dwarves
