The Canals on Mars

http://books.google.com/books?id=QCy6DzgqcI4C&pg=PA66&lpg=PA66&dq=loyd+mars+%22there+is+no+possible+way%22&source=bl&ots=IDuPPpyYDz&sig=9jj5lsIGw5__uPt-2tPXRd8ZgzM&hl=en&ei=YgxVS_WKDtGXtgf82MWtDA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBQQ6AEwAw#v=onepage&q=&f=false

From Sam Loyd:

Here is a map of the newly discovered cities and waterways on our nearest neighbor planet, Mars. Start at the city marked T, at the south pole, and see if you can spell a complete English sentence by making a tour of all the cities, visiting each city only once, and returning to the starting point.

When this puzzle originally appeared in a magazine, more than fifty thousand readers reported, ‘There is no possible way.’ Yet it is a very simple puzzle.

I’ll withhold the answer.