Final answer:
The abdominal viscera located in the retroperitoneum include the kidneys, duodenum, and ascending and descending colon.
Step-by-step explanation:
The organs located in the retroperitoneum are the kidneys, duodenum, and the ascending and descending colon. The retroperitoneum refers to the area behind the peritoneum, which is a lining that holds abdominal organs in place. In this area, the kidneys, duodenum, and parts of the colon remain partially or completely posterior to the peritoneum.