Trekking poles. 20+ years of youthful invincibilty with too many heavy packs over 1000's of miles of rough trail hiking and mountaineering has now started to play havoc on my mid 40's knees...
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock