This puzzle I call "The Rook's Journey," because the word "tour"
(derived from a turner's wheel) implies that we return to the point from
which we set out, and we do not do this in the present case. We should
not be satisfied with a personally conducted holiday tour that ended by
leaving us, say, in the middle of the Sahara. The rook here makes
twenty-one moves, in the course of which journey it visits every square
of the board once and only once, stopping at the square marked 10 at the
end of its tenth move, and ending at the square marked 21. Two
consecutive moves cannot be made in the same direction--that is to say,
you must make a turn after every move.
[Illustration:
+---+---+---+---+---+---+---+---+
| | | | | | | | R |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | | | | | | | |
+---+---+---+---+---+---+---+---+
| | 21| | 10| | | | |
+---+---+---+---+---+---+---+---+
]