Ski resorts use a colored system to grade their runs
Easiest is a green circle
Intermediate is a blue square
Advanced is a black diamond
Expert is a double black diamond
I am an intermediate skier and I'm finding that there are many varying difficulties of blue. In fact I've often seen described "easy blues" and "harder blues." and the real trouble is that the degree of difficulty can vary on the run and the only way you have to learn about it is to try it or have a trusted person who knows your ability tell you about it. The net effect of this is that you find yourself on a run beyond your ability and you feel like a cat in a tree. Fortunately I know how to slide sideways down too steep sections but it's still very disconcerting.
Last friday when leaving Sugarbowl I had a great view of Mt Disney (Jerome Hill where I usually hang out wasn't as clearly visible) and spotted one such blue run that I've been stuck on more than once. I haven't worked up the courage to try it this season but probably will.
Here is a photo with the run on it (click on it to see the annotation). The really troublesome thing about this run is that you've been blissing out on a very nice gentle run and then you get dumped off a cliff. Allegedly there's an easier way down, but I haven't found it yet.