Gingerly I step through the crumbling watchtower at Samatai West and onto the Great Wall of China. I will never forget that first moment. The wall snaking off in either direction as far as the eye can see, the trail undulating up and down along the crest of the mountain ridge. It stops you in your tracks. It takes your breath away. Steep, narrow trails up to watchtowers where guards in centuries past would have watched for invaders, followed by crumbling steps down the other side where we would pick our way carefully and make our way back down.