The Sanctuary is tied to a miraculous event that happened in 1411 in the chapel. One day a priest was serving Mass. At one point during the mass he became suspicious if the bread and the wine really become the body and blood of Jesus Christ. When he got to the part of the mass where the consecrated bread is broken into three pieces, and one of them is put into the chalice, he noticed fresh blood in the chalice. He put the chalice away and quickly finished the mass.
He kept this miracle for himself for some time, but, at the end of his life he gave the chalice to the Parish church of the Holy Trinity in Ludbreg. The Sanctuary in Ludbreg is one of a kind in Croatia and one of the few in the world that was built and acknowledged by Pope Leo X's Bulla (a formal papal letter) on 14 April 1513.
From that time a number of people have miraculously healed in front of the relic. St. Cross Chapel, where the miracle happened, is part of the Batthyany Castle. It is covered in wall paintings of the miraculous transformation of wine into the Most Precious Blood of Christ.
There is also the Croatian Parliament Votive Chapel, built in 1739. The chapel, along with the Way of the Cross, makes a unique permanent outdoor murano glass exhibition.