It was fans and scholars of Tolkien who fingered Lauterbrunnen as the real Rivendell in the '90s, based not only on the descriptions and images that Tolkien provided, but also other clues in the text itself. Notably, in the books, the English name for the river that flows through the valley is "Loudwater," and the Elvish name is "Bruinen."
Loudwater. Bruinen. Lauterbrunnen. Somewhere, the ghost of Tolkien is coyly inserting a pinky into the corner of his mouth and barely suppressing an amused chortle.