Pilgrimages to the "Holy Rock" in Trier Cathedral took place in 1844 and 1891. Over a period of seven weeks in 1844, more than one million pilgrims traveled to Trier. Since 1512, there have been 19 pilgrimages; the most recent pilgrimage was in 2012.
Commemoration of the Holy-Rock Pilgrimages 1844 and 1891, lithograph, 1891, unknown artist; source: Library of Congress, digital ID pga.01945, https://www.loc.gov/pictures/item/2003656870/, public domain.