The original Scala Santa, also known as “Holy Stairway” is the staircase which Jesus ascended during His Passion while proceeding to Pilate’s pretorium.
On November 13, 1893, Pope Leo XIII granted that the faithful who ascend the steps of the Scala Santa on their knees, with a contrite heart, praying and meditating on Our Lord’s Passion, may gain an indulgence of three hundred days for each step. This indulgence is applicable towards the souls in Purgatory. (from : catholic.org)
If you go to Santa Croce a few blocks away from Scala Santa, you could see the relics of our Lord’s passion, the objects used to torture Him, and St. Thomas’ finger who had doubt of His resurrection.