Where are the kidneys primarily located in the body?

The kidneys are primarily located in the abdominal cavity, specifically in the retroperitoneal space, which is the area behind the peritoneum that surrounds the abdominal organs. This placement allows the kidneys to be situated on either side of the spine, typically at the level of the lower ribs. The abdominal cavity serves as a protective space for the kidneys while allowing sufficient functional movement and blood supply.

The other options refer to different body cavities. The pleural cavity contains the lungs, the pelvic cavity holds the reproductive organs and lower gastrointestinal tract, and the spinal cavity houses the spinal cord. Thus, the abdominal cavity is the only correct choice where the kidneys are found.