Start here, the scene takes about 15 minutes (with English subtitles). Then watch the following 10 minutes to the end of the act, where there will be a dramatic battle. (I chose this particular version, from Bayreuth in 1979, because here the singers not only sound great, they also look the part.)
Here‘s the whole story.
The above linked scene is central to the whole story of the 4 mega operas. In this scene, Brünnhilde, Wotan’s daughter and favourite Valkyrie, “grows up” so to speak and does what she thinks is right (and knows that her father really wants) instead of what her father told her to do.
She initially tells Siegmund that he is about to die. But it’s all right, she says. You’re going to Valhalla (the Nordic equivalent of heaven). Siegmund asks some questions about Valhalla, which Brünnhilde answers: Will he be there alone with Wotan (no), will his father be there (yes, but Brünnhilde doesn’t say that Wotan is his father), will a woman greet him fondly there (yes, and not just one). But then he asks: Will his twin sister and love of his life, Sieglinde, join him there (no, and Brünnhilde initially doesn’t say why: Sieglinde is pregnant). Because of the last answer, Siegmund declines the offer and says, if he has to die, he’d rather not go to Valhalla.
What get’s me every time I watch this is the fact that Brünnhilde is the half-sister of Siegmund. She knows it, and loves him dearly. He doesn’t know it. For him, Brünnhilde is a beautiful apparition, but a stranger.
The scene I’ve linked above is well-directed with some great ideas that enhance the storytelling by the music and words. When Siegmund rejects Brünnhilde’s offer to go to Valhalla and says he thinks she is heartless and cold, the actress wonderfully plays the deeply hurt sister.
When she sees Siegmund’s determination not to go to Valhalla (because his great love Sieglinde will not be joining him there), Brünnhilde changes her mind and says that, contrary to what she said before, Siegmund will win the coming battle with his love rival.
When, during the battle, Wotan finds out that Brünnhilde is defying his instructions, he makes sure that Siegmund does die after all, even though it hurts him terribly. He then runs after Brünnhilde, who has fled the scene with Sieglinde.
At the beginning of the next act, we hear the famous “Ride of the Valkyries“.
By the way, JRR Tolkien’s “Lord of the Rings” contains a somewhat similar scene. Similar in that it contains similar archetypes and archetypal relationships. I mean the one where King Théoden dies, with his niece Éowyn by his side to comfort him, who had just before heroically saved him from being devoured by the monster carrying one of the Ring Wraiths. Watch the two-minute scene here.