Fiesta of Our Lady of Guadalupe - December 12

The Feast of Our Lady of Guadalupe is celebrated on December 12th.
In 1999, Pope John Paul II, in his homily from the Solemn Mass at the Basilica of Our Lady of Guadalupe, during his third visit to the sanctuary, declared the date of December the 12th as a Liturgical Holy Day for the whole continent.
During the same visit Pope John Paul II entrusted the cause of life to her loving protection, and placed under her motherly care the innocent lives of children, especially those who are in danger of not being born.

In 1531 a "Lady from Heaven" appeared to a humble Native American at Tepeyac, a hill northwest of what is now Mexico City.
She identified herself as the ever virgin Holy Mary, Mother of the True God for whom we live, of the Creator of all things, Lord of heaven and the earth.
She made a request for a church to be built on the site, and submitted her wish to the local Bishop. When the Bishop hesitated, and requested her for a sign, the Mother of God obeyed without delay or question to the Church's local Bishop, and sent her native messenger to the top of the hill in mid-December to gather an assorment of roses for the Bishop.
After complying to the Bishop's request for a sign, She also left for us an image of herself imprinted miraculously on the native's tilma, a poor quality cactus-cloth, which should have deteriorated in 20 years but shows no sign of decay 479 years later and still defies all scientific explanations of its origin.
It apparently even reflects in Her eyes what was in front of her in 1531.
Source sancta.org