What characterizes the design of a niche in a wall?

The design of a niche in a wall is characterized primarily by its recessed area that serves a functional purpose, such as displaying items. This architectural feature creates a unique space that allows for decorative elements like sculptures, plants, or artwork to stand out against the wall rather than simply being hung or placed on a flat surface. Niches can enhance the visual interest of a room by adding depth and dimension, while also providing an opportunity to showcase collections or aesthetic pieces prominently.

In contrast, the other options do not accurately describe a niche's design. A small area built out from the wall would refer to a protrusion rather than a recess. A large window opening suggests an opening for light and ventilation rather than a display feature. A type of wall mural would imply a painted or decorated surface rather than a built-in design element. Each of these options lacks the specific aspect of being recessed, which is essential to understanding what constitutes a niche in architectural design.