Kalen, I'll agree with you on Sanctuary, and the same can be said of Engh's Pradera. Many people do walk at Pradera, but it's a bit of a hoof. This is an issue with a lot of mountain/front range courses, though certainly not all. Just depends on the property, and the architect, of course.
There's a Jay Moorish course south and west of Denver called Ravenna that is bisected by a ridge of rock that around here is called a hogback. The ninth hole is a dropshot par 3 with the tee up high on the hogback. Traversing that hill is a nasty bit of business with a cart, especially the downhill bits, and walking it with a bag would not be fun. With people around who regularly bike 60 miles a day and the like, I'm sure there are those who walk the course, but most would not. Perhaps for members they have a shuttle cart available just for that part, as the rest of the course wouldn't be a brutal walk. "Unwalkable" is a pretty high standard, although with my fat butt and knee problems, a lot of courses around here fit that description right now........