The app Three Castles is based on a computer game developped by me in 1985.
The game was written in BASIC and published in a book.
In these days computers had not enough memory available to handle detailed pictures, at least not the amount needed for this game.
To overcome this the game was designed to report the page in the book to look at for clues to solve the game.
In the original game commands had to be typed in like:
Go West, Go South
The app version is designed in such a way that you can perform every action with a single tap on the screen:
To solve similar adventure games like Zork or Dungeon one used to draw maps to find your way around.
In the app this is done for you:

The green dot indicates the room you start from, blue dots indicate objects and red ones indicate subjects.
You need the objects to deal with the subjects and solve the game
Some of the rooms (66 in total)