Eithel Nínui, also called the Fountain of Tinúviel, was a fountain found on the plain of Tumladen. It is said to have been created by the tears of Lúthien falling down on the plain when she and Beren were flown over it by Thorondor and his vassals. Its water was recounted in song as having had healing powers until it was destroyed in the Fall of Gondolin.
Note on occurrence
The fountain and its legend is found in one of Tolkien's drafts of the Quenta Silmarillion, but in the published version found in The Silmarillion, Christopher Tolkien omitted it. He has later admitted that this section should have remained in the published work.