Great Rift

Great Rift (大裂け目) is a chasm that runs next to the new dwarven capital, Feo Jera.

Background
For the longest time, this natural barrier had protected Feo Jera from all manner of monstrous attacks. The dwarves could thwart any monsters from the west who tried to invade so long as they defended the suspension bridge which ran across the Great Rift. The suspension bridge over the Great Rift is protected by a fortress. There is apparently an unknown shortcut that bypasses the Great Rift and runs alongside the fortress, which the Quagoa took advantage of exploiting. On the other hand, nobody knew what lies beneath the depths of the Great Rift, and nobody who ventured into it had returned alive not even from the two expeditions that the Dwarf Kingdom sent out to investigate it.

The Craftsman of Dwarf Arc
The Great Rift was the last line of defense that prevented the Quagoa from crossing and taking the dwarven capital. However, somehow the Quagoa led by Yozu managed to find a way around the obstacle and invaded the fortress guarding the rope bridge. The Dwarves at the other end of the gorge were forced to retreat back to the fortress that led to the city as they were pushed back by the huge numbers of the Quagoa.

Just as the Quagoa crossed the suspension bridge and were preparing to break through the fortress gate, they were taken aback when the gates were opened and two of Ainz's Death Knights came out and started to slaughter the invaders. They were forced back to the suspension bridge with the sheer amount of heavy losses from the Death Knight's attacks. Yozu sensing their defeat pulled back his remaining troops and ordered the suspension bridge that connected both sides of the rift to be cut down, so as to prevent the enemy from coming to their side.

While successful in eliminating the two Death Knights, the Quagoa suffered heavy losses and their path to the dwarven capital was cut off, forcing Yozu to fall back to report back in what just happened.

Ainz Ooal Gown would later travel back to the Great Rift to secure the dwarven fortress. Once the fortress was secured, Ainz used the [Mass Fly] spell to fly over the chasm with Shalltear Bloodfallen, Aura Bella Fiora, and Gondo Firebeard in order to travel to Feo Berkana.

Layout
It referred to the huge chasm that ran along the western side of the Dwarven Capital, Feo Jera. It was a massive crevasse, over 40 miles long and 130 yards across at its narrowest point. Its depth was unknown.

Trivia

 * Ainz Ooal Gown wishes to do an in-depth investigation of the Great Rift, believing unknown monsters and ores to be found there.
 * It was never explained how the Quagoa managed to circumvent the Great Rift.
 * Dwarf Kingdom's Commander-in-Chief thought the Dwarves had maybe grown arrogant, believing that they will be okay as long as they have the fortress at the Great Rift.