Also here's a master study of an untitled watercolour painting by David Roberts.
Time spent would be 2 1/2 hours ish.
The reason I chose this was because I liked the large contrasts and harmonic colours. When I first started the study I almost thought there were only a total of four colours in this piece, namely orange, brown, black, and blue. I quickly saw there were many slight variations of these, but mostly It's a mix of the named colours with a splash of extra orange and white added specifically on the main gate the boats are entering.
There is a rythmic quality to the gates placement. The idea of gates is that they're meant to pass through, and you can sort of "pass though" all the three gates in one sweep of the eye. This concept is further enforced by having boats sitting next to all the gates. There's also rythmic details in the gates themselves, like the back one with the choppy vertical lines, followed by the wavier pillars, and even the negative space inbetween.
In the bottom right corner there's some stones, which just as the boats and gates, comes in three levels, and they slope roughly the same way as the gates, and almost echoing the perspective of the giant wall. The stones also serves as a framing, both for literally the corner of the painting, but also in sense of depth. It marks the closest area so that we know where we're seeing this landscape from and get a clearer sense of space. Its highlights also point directly towards the wall, creating a contrast in direction.
In fact there's a lot of playing with direction here as well. Horizontal lines are long and bold on the right hand side, but shorter, more subtle on the left side. Conversively there are more and bolder vertical lines on the left side. This is what makes the directional contrast of the sail of the center boat so apparent.
However, by far the best thing is the dude donning three hats!