This building serves as a home to the main protagonist, Quasimodo. By law, it serves as a refuge for those who are persecuted. Examples of this include when Esmeralda was in trouble with the law and had to stay in the cathedral, she sings "God Help the Outcast" her song also lured Quasimodo, but before he could talk to her just after finishing singing the song, a parishioner who mistook him causing trouble shouts at him causing him to knock down a candlestaff and flees back to the belltower. Esmeralda was alerted by the Parishioner's shouts and follows Quasimodo, the parishioner also attempts to stop her and Djali from following him and is promptly scolded by the Archdeacon and when Quasimodo saved Esmeralda and called for sanctuary. Frollo and his soldiers attempted to break down the doors and lead the enraged citizens of Paris and French army to attack, leading Frollo's soldiers to their defeat at the hands of those within. In the films, Quasimodo seems to have a certain attachment to Notre Dame, despite his newly-found allowance of being able to interact with Parisian society. Quasimodo likely still views the cathedral as a home.
In Real Life
Notre Dame de Paris, also known as Notre Dame Cathedral, is a Gothic, Catholic cathedral on the eastern half of the Île de la Cité ("Island of the City") in the fourth arrondissement ("Administrative District") of Paris, France. It is the cathedral of the Catholic Archdiocese of Paris: that is, it is the church that contains the cathedra (official chair) of the Archbishop of Paris.
Notre Dame de Paris appears in two occasions. In its first appearance, Linguini passes by on his bike while on his way to kill Remy as per Skinner's instructions. In its second appearance, Linguini and Colette pass by the cathedral while rollerskating.
Mater, Finn McMissile and Holley Shiftwell drive by the cathedral after their arrival in Paris.