There is a lot of benefit and great spiritual reward in visiting the grave of Imam Husayn [a]. The Prophet [s] has said of his grandson Imam Husayn [a]: "Husayn is of me and I am of him". Several narrations mention that visiting the grave of Imam Husayn [a] relieves one of worldly afflictions as well as those after death.
Believers, therefore, come from all parts of the world all year round to receive the honour of visiting Imam Husayn [a], particularly during the first ten days of Muharram (Ashura) and the twentieth of Safar (the fourtieth).
One common Iraqi custom during that season is to go walking from Najaf to Karbala, reflecting their strong adhesion to and adoption of the morals and principles for which Imam Husayn [a] struggled and attained martyrdom.
source : http://www.al-islam.org
