Pope Francis visits the Knock Holy Shrine in Co Mayo, which is revered by many Irish Catholics.
Maria Casey, marketing and communications manager at Knock Shrine, explains the meaning behind the pilgrim site.
"Knock Shrine is a special place in Co Mayo in the west of Ireland because of the appearance that took place here in 1879.
"An appearance of 15 people from the village of Knock appeared on August 21. At that time, Knock was a small, rural village.
"Around 20.30 hours 15 people saw a light coming from the parish church, so they went to the wall of the facade to see what it was.
"They saw the appearance of Our Lady, Saint Joseph, John the Evangelist and a lamb.
& # 39; They said the appearance lasted two hours.
& # 39; They all recited the rosary and after the apparition the news spread very quickly. Each of these witnesses was asked to give a testimony to a committee of inquiry.
– Knock Shrine (@knockshrine) August 24, 2018
"There was an investigation a few months later and then people started to descend on Knock – it spread to newspapers in Ireland, England and America.
"People started coming here in the hope of getting a cure, and Knock became synonymous with that, and people came to the site of the apparition to get some clay or holy water to send abroad.
"It has evolved over the years and it has a very unique story in the sense that it is the only sanctuary in the world where the Lamb of God has appeared.
"It is not only a Maria sanctuary, but also a Eucharistic sanctuary.
"People have a special affinity with the place.
"It has a wonderful atmosphere and that attracts people."
– Press Association