The two most famous paintings by Caspar David Friedrich hang side-by-side in the Alte Nationalgalerie in Berlin: “Mönch am Meer” (Monk by the Sea) and “Abtei im Eichwald” (Abbey Among Oak Trees). Both were exhibited in 1810 and propelled Friedrich to fame when the king of Prussia bought both. Lean in closely to see the gulls warning the monk and the birds in the window of the ruined church.