100名城 旅行記 is an iPhone app developed by Green Speed Inc. that allows castle enthusiasts to keep a record of their travels. The app lets users collect and track the 100 most famous castles in Japan, with a "conquered" flag that appears after visiting each one.

The app's features include the ability to view basic information about each castle, mark favorite castles, check off visited castles, create a collection, and easily create travel logs with photos and text. The app also includes a memo feature for users to jot down notes during their travels. With its user-friendly interface and comprehensive features, 100名城 旅行記 is a must-have app for anyone who loves castles and traveling in Japan.