The Langwell (not to be confused with the Langflood), is a river in Rhovanion. It flows down eastwards from the Misty Mountains in western Elderslade, though its upper stretches are inaccessible do to impassable terrain. From there, it flows into the Dvergvát, and then on into the western fall of the Twainmantle. The Langwell is one of the two main rivers, along with Greylin, that meets in the northern Wells of Langflood to form the beginnings of the Anduin.
In T.A. 1977 Frumgar led the Éothéod from the middle to the upper part of the Vales of Anduin, to escape from the growing shadow of Dol Guldur and to take advantage of the fall of Angmar in 1975. Upon their arrival they built their capital city of Framsburg (named after Frumgar's son Fram) between the Langwell and the Greylin. The Éothéod left the vicinity of the Langwell in T.A. 2510 when they became the Rohirrim, settling in Rohan.
The upper course of the Langwell is unknown, but it arises in the Misty Mountains, not the Grey Mountains. It may be that this river south of Gundabad is the Langwell.
The Langwell is known to be a longer river than the Wyrmsgráf River to the east. This river flowing from the south of Dvergvát may alternatively be the Langwell.
Either way, the part of the Langwell that is seen entering the Dvergvát must be but the very end of the upper part of the Langwell.
Part of the Langwell's flow, the Dvergvát is a lake lying southeast of the gates of Gundabad.
The Langwell then plummets off the high cliffs of Elderslade into the Wells of Langflood far below.
The Langwell fall is the leftmost of the Three Sisters of Framsburg, their mist perpetually covering the Misthallow.
The two falls of the Langwell and the Wyrmsgráf River together are known as the Twainmantle.
The Langwell then follows the base of the plateau of Framsburg through a mist-cloaked valley.
This dramatic setting is thus the creation of the longest river in Middle-earth, with the Langwell as one of its main sources.