It's almost impressive how little Daemon Targaryen (Matt Smith) has actually done this season of House of the Dragon, but he's certainly seen some things.
Ever since he arrived at Harrenhal for what has to have been the easiest conquest ever, Daemon has been having some pretty strange hallucinations — including a young Rhaenyra (Milly Alcock), a sex dream about his dead mother Alyssa (Emeline Lambert), and glimpses of his half-rotten brother Viserys (Paddy Considine).
In the finale, though, Daemon has a different type of vision — a glimpse into the future, rather than the past. So what exactly does he see, and what does it mean?
When Daemon touches Harrenhal's weirwood tree, he sees a fast cut of images that will be familiar to Game of Thrones fans: Brynden Rivers, also known as Bloodraven, the Targaryen bastard and greenseer who acts as Bran Stark's mentor; a shot of the White Walkers standing in the woods; a glimpse of a dead dragon (possibly Daemon's own Caraxes?) on a battlefield littered with bodies; Daemon himself falling into a body of dark water; and finally everyone's favourite Targaryen conqueror Daenerys (Emilia Clarke), sat covered in ash and holding her dragons in a flash back (or, in the timeline of the story, a flash forward) to the Game of Thrones moment where she becomes a literal Mother of Dragons (a moment foreshadowed in episode 3, when Rhaena Targaryen (Phoebe Campbell) is sent away with the dragon eggs that Daenerys will come into possession of over a century later).
After this quick-cut, Daemon walks into the throne room and sees Rhaenyra sitting on the Iron Throne. Helaena (Phia Saban) then appears behind him. "It's all a story," she says, "and you're but one part in it. You know your part."
Given that we're armed with the knowledge of what happens in Game of Thrones, it's pretty clear that Daemon is being shown a glimpse of what Aegon I saw in his much-discussed "Song of Ice and Fire" dream: the threat of the White Walkers in the north, and the need for Westeros to unite behind a Targaryen ruler on the Iron Throne to stop them.
Interestingly, Daemon also appears to have been given a glimpse of how he fits in to this picture. Harrenhal witch Alys Rivers (Gayle Ranking) has already told him that he'll die at Harrenhal — could the vision he sees of the battlefield and the dead dragon, followed by the shot of himself falling into water, be a vision of his own death? If so, Daemon's vision also makes it clear who he'll be dying for when he's shown a glimpse of Rhaenyra on the Iron Throne.
This seems to be why he ultimately decides to take the knee before Rhaenyra when she shows up at Harrenhal, and put his own desires aside — he's been scared by what he saw in the vision and, as Helaena says, he now knows his part in the story.