The Hunchback of Notre Dame

In 1482 Paris, Clopin, a gypsy puppeteer, narrates the origin of the titular hunchback. A group of gypsies sneak illegally into Paris, but are ambushed by Judge Claude Frollo, the minister of justice. A gypsy woman in the group attempts to flee with her deformed baby, but Frollo chases and kills her outside Notre Dame. He tries to kill the baby as well, but the cathedral's archdeacon intervenes and accuses Frollo of murdering an innocent woman. To atone for his sin, Frollo reluctantly agrees to raise the deformed child in Notre Dame as his son, naming him Quasimodo.
Twenty years later, Quasimodo develops into a kind yet isolated young man who has lived inside the cathedral his entire life. A trio of living stone gargoylesâVictor, Hugo, and Laverneâserve as Quasimodo's only company, and encourage him to attend the annually-held Festival of Fools. Despite Frollo's warnings that he would be shunned for his deformity, Quasimodo attends the festival and is celebrated for his awkward appearance, only to be humiliated by the crowd after Frollo's men start a riot. Frollo refuses to help Quasimodo, but Esmeralda, a kind gypsy, intervenes by freeing the hunchback, and uses a magic trick to evade arrest. Frollo confronts Quasimodo and sends him back inside the cathedral.
Esmeralda follows Quasimodo inside, only to be followed herself by Captain Phoebus of Frollo's guard. Phoebus refuses to arrest her for alleged witchcraft inside Notre Dame and instead has her confined to the cathedral. Esmeralda finds and befriends Quasimodo, who helps her escape Notre Dame out of gratitude for defending him. She entrusts Quasimodo a pendant containing a map to the gypsies' hideout, the Court of Miracles. Frollo soon develops lustful feelings for Esmeralda and, upon realizing them, begs the Virgin Mary to save him from her "spell" to avoid eternal damnation. When Frollo discovers that she escaped, he instigates a city-wide manhunt for her which involves setting fire to countless houses in his way. Phoebus is appalled by Frollo's evil reputation and defies him. Frollo then sentences Phoebus to death. Phoebus is struck by an arrow and falls into the River Seine, but Esmeralda rescues him and takes him to Notre Dame for refuge. The gargoyles encourage Quasimodo to confess his feelings for Esmeralda, but he is heartbroken to discover she and Phoebus have fallen in love.
Frollo returns to Notre Dame later that night and discovers that Quasimodo helped Esmeralda escape. He bluffs to Quasimodo saying that he knows about the Court of Miracles and that he intends to attack at dawn. Using the map Esmeralda gave him, Quasimodo and Phoebus find the court to warn the gypsies, only for Frollo to follow them and capture all the gypsies present. Frollo prepares to burn Esmeralda at the stake after she rejects his advances, but Quasimodo rescues her and brings her to the cathedral. Phoebus releases the gypsies and rallies the citizens of Paris against Frollo and his men, who try to break into the cathedral. Quasimodo and the gargoyles pour molten lead onto the streets to ensure no one enters, but Frollo successfully manages to enter. He pursues Quasimodo and Esmeralda to the balcony where he and Quasimodo both fall over the edge. Frollo falls to his death in the molten lead, while Quasimodo is caught by Phoebus on a lower floor. Afterward, Quasimodo comes to accept that Phoebus and Esmeralda are in love, and he gives them his blessing. The two encourage him to leave the cathedral into the outside world, where the citizens hail him as a hero and accept him into society.

Question: How does Frollo discovers the Court of Miracles?