A Sturdy Walk is a series of 12 caches forming a circular walk of about 4 miles placed to coincide with the 2008 Dreaming Spires Cache Bash at Sturdys Castle. This is a family friendly walk (although you may struggle with a buggy in some parts) with not too much in the way of hills and roads, and no Micro's 
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In the cache you will find a letter and a number which you should take note of and use it to help you find the Bonus cache.
On the homeward stretch now . Walk south along the National Cycle Route 5 until you have nearly reached the point where the paths cross. You should now have all the info you need to find the bonus, now go get it.