This painting of the Grand Canal in Venice by Richard Parkes Bonington (1801-1828) looks immensely detailed and at first it looks like it would have taken a long time to paint. But he used a time-saving method that works really well for both plein-air and studio paintings of architecture. The trick is to paint the large areas of the building fronts in opaque paint with big bristle brushes. Then let that dry completely. This might take 24 hours or several days, depending on whether there's a drying agent in the paint, such as Liquin or a drop of cobalt drier. On the second day's session, you can go back over those big areas with a smaller brush to subdivide the building fronts.