Many of the passages in The Ring when it is a male/female theme or duet - when Wotan is singing farewell to Brunhilde, after he has stripped her of her powers, and placed her in the magic fire, for example.
The most erotic passages in classical music
Wagner has written the overture to Tannhäuser with a sensuous, sensual, erotic connotation in mind. Ravel's Bolero, parts of Berlioz' Symphonie Fantastique are downright sexual. But I don't want this to be the point here. What I'm after are "erotic passages", which are full of senuality and would induce images in kind, or a feeling in kind or a yearning in the listener. I also wonder, if there are any gender differences in what music is deemed erotic. Erotic, nota bene, not sexual!