This one of a series of paintings Monet did of the Rouen Cathedral in Rouen, France. Monet painted many different versions of the Facade due to his obsession with how light affected the object at different points of the day.
Monet painted this image with a lot of quick brush strokes. When up close you can see each individual brush mark with a particular color but when you step back all of the brush strokes blend together. The way the blues, yellows and whites blend together on the structure really convey the warmth and brightness of the sunlight at that particular moment.
This painting is a prime example of why Monet is one of the greatest impressionist. He uses just the right amount of abstract, in terms of colors and realism to give the viewer not only a visual representation but it also invokes a sense of feeling the sunlight on your back, as if you where there.