An FFGL effect that reads the picture's brightness as ground height and draws it like a survey map: contour lines at a fixed interval, heavier index contours, hill-shading from the north-west, hypsometric tints, and a sea the music can raise. Contours crowd together on steep ground because their spacing is the slope, and every line stays one pen width whether it's on a cliff or a plain.
This demo runs the plugin's shaders in your browser, so it needs JavaScript and WebGL2. The plugin itself, its source and its downloads are on its repository.