--aah. Right. One day he spies this old lady at the foot of the tower-- she's the enchantress who's been keeping Rapunzel up there in the first place, you know? And she's the only one who comes and goes from the top. She calls up to Rapunzel those lines: "let down your hair, so that I may climb the golden stair". Like a password between them. And the prince sees all this and decides he's gonna try it too.
So he does, and gets up there, and they finally meet each other.