Abbey among Oak Trees (1809 or 1810) by Caspar David Friedrich.
More from the Google Art Project. In these views we get to see some of the subtleties in the work of Caspar David Friedrich (1774–1840), a master at rendering fine gradations of light and shade. The paintings are from the Alte Nationalgalerie, Berlin, and Google’s photographs look far better than any book reproductions I’ve seen (assuming you have a decent monitor).
Moonrise over the Sea (1822) by Caspar David Friedrich.
Solitary Tree (1822) by Caspar David Friedrich.