Thereafter it is said that magic and destiny led him on a day to a cavernous opening down which a hidden river flowed from Mithrim. And Tuor entered that cavern seeking to learn its secret, but the waters of Mithrim drove him forward into the heart of the rock and he might not win back into the light. And this, it is said, was the will of Ulmo Lord of Waters at whose prompting the Noldoli had made that hidden way.
