Complex sentence: Shias make pilgrimage to the Imam Husayn Shrineas it is one of the holiest places for Shias outside of Mecca and Medina, with up to a million pilgrims visit the city to observe the Day of Ashura, the anniversary of Husayn ibn Ali's death.
Split into simpler sentences: Shias make pilgrimage to the Imam Husayn Shrine as it is one of the holiest places for Shias outside of Mecca and Medina. Up to one million pilgrims a year visit the city to observe the anniversary of Husayn ibn Ali's death.