Not being a great fan of opera, I have never sat through Wagner’s famous opera. However, I always enjoyed the musiv-to me the song of the nightwanderer is one of the most hauntingly beautiful melodies ever composed. My question: who is the nightwanderer, and why does he wander? 
The only thing that I know about Tannhauser are the ‘C-beams glittering in the dark near the Tannhauser Gate’.
I’m only vaguely familiar with the entire opera, but Googling doesn’t turn up a character by that name. Got a first line, in English or German?
The last section of Richard Strauss’s “Thus Spake Zarathustra” is titled exactly “Song of the Night Wanderer”. But the whole piece is instrumental only, no people singing.
As to who that Night Wanderer is, read the book. 
I’m moderately familiar with Tannhäuser, and I don’t think there’s a night wanderer in it. The only wandering done is Tannhäuser wandering to the Venusberg and back again, then wandering to Rome with a group of pilgrims (who sing the well-known pilgrims’ chorus) and back again.
It occurs to me that Wagner’s Flying Dutchman is sometimes refered to as “The Wandering Jew”. I’m not into the philosophy, but the scene where the Hollander’s dead crew outsings the other guys at beer drinking is cool. 
Here is one page at Amazon with some track samles. Is one of those the motive that you refer to?
“Hauntingly beautiful” to me describes the Pilgrims’ chorus Beglückt darf nun dich, o Heimat, ich schauen, FWIW. (this is a recurring motive, also in the overture). It that perhaps the one that you mean?