The Week reports, back in October 2012:

An ambitious new e-book pushes the boundaries of interactive fiction by requiring readers to visit specific locations to unlock new parts of its story
If you want the full experience of The Silent History — a new e-book available on the iPhone and iPad — you’d better get ready to do some traveling. The Silent History is “part medical case study, part mystery novel, and part-real-life scavenger hunt,” says Sarah Hotchkiss at KQED, and the e-book aims to personalize its narrative for each reader. (Watch a trailer for The Silent History below.) The Silent History is divided into two parts: Testimonials and field reports. The testimonials, which are divided into six volumes of 20 chapters each, are automatically unlocked as the story unfolds each day. But the field reports require an unprecedented level of interaction: They can only be read by traveling to specific locations, and readers are encouraged to write and contribute their own localized installments.

Full Story: Yahoo News: The Silent History: The strange new e-book that makes you travel to read it

(Thanks Skry)