"Some visions of ghosts could actually be souls in purgatory that are seeking prayers. We must never forget to pray for our brothers and sisters in purgatory. We should offer our mass to them every time we attend." [source]
When in Rome, make sure to visit the Museum of the Souls of Purgatory. "Located in a small room next to a church, this eerie museum displays objects and photos of objects said to show traces of apparitions who reside in Purgatory."