What feature in a columbarium is specifically designed for individual placement of ashes?

A columbarium is a structure specifically designed to hold cremation urns. The feature particularly intended for the individual placement of ashes within a columbarium is known as a niche. Niches are compartments or recessed areas where urns containing cremated remains can be securely stored. Each niche is usually marked with a plaque or inscription to recognize the individual whose ashes are contained within it, making it a personal and respectful space for memorialization.

In contrast, urn vaults are containers designed to encase urns for additional protection, but they do not serve as a display or memorial space within the columbarium. Grave markers and burial plots pertain to traditional burial practices and do not apply to the cremation and inurnment context associated with a columbarium. Therefore, the niche is the correct answer, as it distinctly accommodates individual placements of ashes.