The Ratanur Trap is a deep canyon in the middle of Vetoubahr. It has long been avoided by Azrik's peoples. There no roads or paths going into it, and a two mile drop into a lake once prowled by aquatic demons is more than enough to keep most away.
In the Demon Spawn War (8972 GE - 9493 GE), a rift was opened at the tip of Moredhel. This rift was a link Kurun'Ush, a world under the control of the demon lord Gorag'theg. Later to be known as the Moredhel-Fihrgrell Rift, opened on 3 Temporal 9266 GE, on one side was an abyssal ocean, the other a soon-to-be flooded valley. After the initial wave of water, the flow steadied, becoming a river of seawater that went down the valley then northwest to fill the Ratanur Trap then onward to the sea.
In 9274 GE, engineers under the Covenant general Abbathor planted a null mine, creating a counter to the Moredhel-Fihrgrell Rift. This second rift, beneath the floor of the then submerged Ratanur Trap, was the Fihrgrell Drain. When it was opened, the canyon drained, then the water flowing over in waterfalls was drawn through the Fihrgrell Drain then back to the abyssal world it came from. The river continued to flow out of the upper rift for eight years, contained to flowing down the valley then into the rift at the bottom of this canyon. When Thyrm stoppered the upper rift with the The Frozen Titan, the river of seawater flowing in came to an end.
Today, the bottom of this canyon is a salty lake, which because of its depth, is considered more an Underdark area than of the surface. Lake Dynaer is the remnants of Fihrgrell's seawater that flowed through the Moredhel-Fihrgrell Rift.