The Hanging-cloud Bridge at Mount Gyōdō near Ashikaga (Ashikaga Gyōdōzan kumo no kakehashi), from the series Remarkable Views of Bridges in Various Provinces (Shokoku meikyō kiran) — jigsaw puzzle
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Measured from the picture: how many of its pieces look like other pieces. A wide stretch of sky or water takes far longer than a crowded street at the same piece count.