A colonoscopy is a procedure to look at the inside of the colon. The colon is the large intestine and the last part of the digestive system. The colon dries, processes, and eliminates the waste left after the small intestine has absorbed the nutrients in food. The colon is about 3 to 5 feet long. It travels from the lower right corner of the abdomen (where the small intestine ends) up to the liver, across the body to the spleen in the upper left corner and then down to form the rectum and anus.