Proper Mountaineering

On Sunday there's a special hiking festival going on in town; the school are paying for ten of us to take part so how could I say no? It was initially said to be 8km, which is not so bad as we did about 5km last time anyway. Apparently it's actually 12km, which is a little more daunting but should be okay. And there's a prize for first to the top, which is nice, but with a thousand people taking part I won't get my hopes up too much. The odd thing is that we each have to take up 2kg of soil with us. Altogether that's like 2 tons (if you were struggling with the math). There is no explanation given as to why, so your guess is as good as mine. I'll let you know.