"'You'll know that one, the Pilgrims' Chorus.'"
The Pilgrims' Chorus is a choral piece at the end of Act III of Richard Wagner's opera Tannhäuser. It is also played as an orchestral piece at the beginning of the opera's overture.
Listen here to the overture to Tannhäuser on Spotify.
Lister here to the Pilgrim's Chorus from Act III of Tannhäuser on Spotify.