FROM THE NORTH bank of the river, in Portugal's remote upper Douro Valley, the water reflects the mountain like a looking glass. Waiting on a small jetty used to moor the handful of vessels that cross this stretch of the river, one is struck by the stillness of the morning. Silence. Up here there is no mobile signal, no hum of traffic to break the calm. The only indication that this is harvest time, one of the busiest periods of the year, is the faint bustle on the far shore as the ovens are lit in the pickers' quarters in preparation for breakfast.

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