The two main tourist attractions located within Kochi's city center are the Sunday Market and Kochi Castle.
The former is a 1 km long chain of outdoor tents and stalls, all selling locally grown meat, fish, and produce at insanely low prices. There are a few stalls that sell souvenirs, such as Kochi's famed kitchen knives, as well. From a distance, the entire set-up is remarkably reminiscent of a homeless tent city.
While it may not be everyone's cup of tea, I found it fun to stroll past the stalls and examine all the strange and unusual vegetables. 10 points if you've heard of an indigenous Japanese ginger shaped like a tulip bulb, known as "myoga".
Despite being a bit on the small side, Kochi Castle is well worth a visit. It is known as one of Japan's 12 "intact" castles. This means that all of the inner buildings and castle keep are still in their original pre-Meiji Restoration form, dating back to 1729.