The Church has not officially claimed that Christ's body was wrapped in the shroud, preferring instead to focus on what it means to those who see it.
"Whether you believe or don't believe, there is no doubt it is something special," an Italian man who was among the first visitors on Sunday told the AFP news agency.
Earlier this week, Archbishop of Turin Cesare Nosiglia said: "What counts the most is that this shroud... reflects in a clear and precise manner how the gospels describe the passion and death of Jesus.
"It is not a profession of faith because it is not an object of faith, nor of devotion, but it can help faith."
Archbishop Nosiglia said that many of those coming to see the shroud would be returnees.
"That means there is a fundamental need in people's hearts to renew this incredible experience that they had the first time they saw it," he said.
"Even non-believers will come. It's an occasion that brings everybody together."