The diagram represents the passages or galleries in a mine.
Every passage, A to B, B to C, C to H, H to I, and so on, is one furlong in length. 
There are thirty-one of these passages. 
An official has to inspect all of them, and he descends by the shaft to the point A. 

How far must he travel, and what route do you recommend? 
Try to find the shortest route.