Final answer:
The kidneys are located in the retroperitoneal space, on either side of the spine. They are roughly the size of a fist and are positioned between the parietal peritoneum and the posterior abdominal wall.
Step-by-step explanation:
The kidneys are located in the retroperitoneal space, which means they are located behind the peritoneum, the membrane that lines the abdominal cavity. They are positioned between the parietal peritoneum and the posterior abdominal wall. The kidneys are roughly the size of a fist and are located on either side of the spine, with the right kidney slightly lower than the left due to the asymmetry caused by the liver.