To reach Lucrecia’s cave, Cloud and the others must have acquired a chocobo that can climb mountains (a green, black, or gold chocobo). By climbing over the mountains east of Nibelhein, Cloud finds a circular lake with a waterfall at the north end. Behind the waterfall lies the cave. Another way to reach the cave is to acquire a submarine and explore underwater until one comes to a long submerged cavern that ends at the circular lake where the submarine can emerge.
For Lucrecia to appear in the cave, Vincent must be in the party at the time. Otherwise as Cloud enters she speaks the name “Vincent” or “Sephiroth” but the cave is empty.
Vincent and the party enter a crystalline cave hidden behind the waterfall.
Lucrecia: “Vincent…”
Vincent: “That voice? It can’t be… Lucrecia..?”
Lucrecia: “Vincent..?”
Vincent: “Lucrecia!”
Lucrecia: “Stay back!!”
The screen fades in a bright light, then the scene changes to a flashback to Nibelheim. Gast, Lucrecia and Hojo enter the Shinra Mansion. Vincent stops outside the mansion's gates.
The scene changes to Vincent walking and talking with Lucrecia near the Nibelheim well. They reach the town’s entrance and Vincent clasps Lucrecia’s hands and says something to her. Lucrecia quickly breaks Vincent’s hold and runs away. Vincent extends his hand in a “wait!” gesture.
The scene changes to Lucrecia hugging (and perhaps kissing) Hojo at the entryway to Nibelheim. Vincent sees them, shakes his head in defeat, and walks away.
Vincent: “If she is happy then… I don’t mind.”
The scene changes to Lucrecia’s room at the town inn. She is sitting in a chair rubbing her stomach.
The scene changes to the basement lab. Vincent and Hojo are arguing in front of Lucreica. Vincent gestures angrily with his hands.
Vincent: “I’m against it! Why experiment on humans!”
Hojo: “She and I are both scientists!”
Lucrecia bows her head down in what may be shame or defeat.
Vincent (narrating): After that, a child was born to Lucrecia…
Vincent (narrating): That child’s name is… Sephiroth…
Lucrecia walks a few steps then collapses in her room at the inn.
The scene changes to the lab. Vincent confronts Hojo and appears to be yelling at Hojo. Hojo grabs his head, looking frustrated, and then shoots Vincent. Vincent tries to hold his arm out towards Hojo, but he falls to the floor, apparently dead from the shot.
The scene changes to Hojo experimenting on Vincent, who lies unmoving on a table in the lab.
The scene changes to Vincent awakening. Hojo is not in the lab. Vincent gets off the table, looks up, and raises his hands.
Vincent: Urrrg!!!! (There is a weird growling sound effect in the background)
The screen fades to black.
Vincent (narrating): This body is… the punishment that’s been given to me.
Vincent (narrating): I was unable… to stop Professor Gast and Hojo…
Vincent (narrating): And Lucrecia… I was unable to stop them...
Vincent (narrating): All that I was able to do was watch… that is my punishment
The scene fades back to the crystalline cave.
Vincent: “Lucrecia… You’re alive…”
Lucrecia: “I wanted to disappear… I couldn’t be with anyone… I wanted to die…”
Lucrecia: “But the Jenova inside me wouldn’t let me die…”
Lucrecia: “Lately, I dream a lot of Sephiroth… My dear, dear child. Ever since he was born I never got to hold him, even once… Not even once.”
Lucrecia: “You can’t call me his mother… That…is my sin…”
Vincent steps toward Lucrecia in what may be an attempt to comfort her.
Lucrecia: “Back!! Stay back!”
Lucrecia: “Vincent… Won’t you please tell me?”
Vincent: “…What?”
Lucrecia: “If Sephiroth is still alive? I heard that he died five years ago. But I see him in my dreams so often… And I know that physically, like myself, he can’t die so easily.”
Lucrecia: “Please, Vincent, tell me…”
Cloud moves forward to speak, but Vincent blocks Cloud with his arm.
Vincent: “Lucrecia… Sephiroth is dead…”
The cavern dims and everything fades out. When the screen lights again, the party is standing outside of the cave. If you try to reenter the cave, Lucrecia has disappeared.
Note: During the dialog Lucrecia’s speech bubbles were slightly transparent, whereas everyone else had normal, solid colored speech bubbles. This may imply that Lucrecia is a spirit or some other entity and not fully “alive” or “human.”
Screenshots are courtesy of Raven. Check out her website here.