Today, if one fulfills the conditions, the faithful can gain the plenary indulgence of the Portiuncula (or Porziuncola) - the chapel of Our Lady of the Angels in Assisi which St Francis started to repair in fulfilment of the Divine command to "rebuild my church." There is more about the history of the chapel and the indulgence here.
To obtain the indulgence one must visit any parish church in the world, recite an Our Father and a Creed for the Pope's Intention and make one's Confession and receive Communion within eight days either side of the visit, as well as being free from attachment to even venial sins. If there is still attachment to such venial sins then the indulgence is partial rather than plenary.
So I'm off to recite the Pater and the Credo at the Oratory today.