At first, when she retired from a lifelong career in nursing in her native Spain, Joanna Perez Osuna struggled with a lack of purpose. Then she found solace in a virtual world populated by "Pikachus," "Weedles" and "Smeargles."
Perez started playing Pokemon Go, the augmented-reality game that encourages players to travel around looking through their mobile phone cameras so they can collect animated creatures that "appear" in front of them.
Now the 75-year-old spends up to six hours a day walking the streets of Badalona, a quiet Spanish town to the north of Barcelona, chasing after digital ghosts, dragons and monsters.