Which type of service would likely not involve an above-ground structure?

Green burials typically do not involve any above-ground structures. This method of interment emphasizes environmental sustainability and natural decomposition, and it often involves the use of biodegradable materials for the casket or shroud. In green burials, the body is buried directly in the earth, usually in a simple grave that is not marked by a heavy monument. This approach aligns with the principles of minimizing environmental impact and preserving the natural landscape, and it contrasts sharply with the other options listed, which all involve some form of above-ground structure.

Mausoleums, columbaria, and niches all require architectural features that specifically accommodate above-ground interments. Mausoleums are buildings designed to house the deceased in a way that is visible and accessible, while columbaria are structures designed for storing urns containing cremated remains. Niches, which are compartments within columbaria or cemetery walls, also serve to hold urns above ground. Thus, green burials are unique in their avoidance of any constructed above-ground elements, aligning them with natural burial practices.