Why do this problem?
can be fun to do and the pupils will be doing a number of calculations - probably without them realising it. It has the facility to be extended very easily. This problem provides children with the opportunity to make sense of numbers and reason about them. Systematic working is also involved.
How did you decide on your route?
Ask the pupils to invent new ones and ask them how they make them harder/easier.
Some templates of the 4 by 4 square could be useful.