Kochi was formerly known as Tosa (土佐).
Pint-sized Kōchi Ryōma Airport (IATA: KCZ)  has flights to Osaka-Itami, Osaka-Kansai, Tokyo-Haneda, Nagoya-Komaki and Naha (Okinawa). Buses to/from Kochi station (35-45 min, ¥700) leaves roughly twice an hour.
The most popular way to arrive in Kochi by train is from Okayama, which is on the main island of Honshu. From Okayama take the Limited Express Nanpu train, and you will arrive in Kochi in approximately 2.5 hours.
There are several night buses from Tokyo, Osaka and Fukuoka to Kochi, and one from Osaka to Nakamura and Sukumo through out the year, as well as special bus services during the Bon festival in early August. There are also day time buses from other cities in Shikoku, as well as from Hiroshima. http://www.jr-shikoku.co.jp/bus/
There are car rental stores at Kochi, Nakamura and Susaki and Aki train stations, as well as at the airport. Kochi roads can be long, narrow and winding, the drivers careless and signs difficult to understand without knowing Japanese, but driving is the best way to see most of the far flung sites throughout Kochi.
There is an expressway running down from Otoyo town, on the northern border, passing through Kochi city and heading down towards Susaki. Construction is underway to extend this as far as Shimanto city.
Even on the new Gomen-Nahari line, trains are few and far between, and do not always connect to buses and tourist sites very well.
If you are in Shikoku for a while, or even making one return train journey it's worth getting a Young Weekend discount card from JR. The card costs ￥1000 for a year and gives a discount of up to 40% on return journeys made on a single weekend. The card is only available for passangers 29 years and younger.
Look out for the 'anpanman trains' they're just regular trains but they're painted throughout with the characters from the popular anime 'anpanman'
The JR Shikoku website has a lot of information (in Japanese) on trains in Shikoku, as well as connecting buses, airport buses, hotels and tourist attractions. http://jr-shikoku.co.jp
The Harimaya Bridge
The local specialty is katsuo no tataki, bonito quickly seared under high heat so the surface is cooked while the inside is still raw.
Liquor in all forms: the people of Kochi are known as the biggest drinkers in Japan. The women in Kochi are particularly renowned for their affinity and ability to drink. They are refered to as Hachikin, literally meaning 8 testicles since it is said that one Tosa (Kochi) woman can drink like four ordinary men. Kochi offers an abundance of locally made sake and shochu, and the friendly locals will surely approach you for a fun interaction at Kochi`s numerous bars.
17 sake breweries in Kochi make Tosa Space Sake (土佐宇宙酒 Tosa uchūshu), prepared with yeast that was taken into space for ten days and back aboard a Soyuz rocket in 2005, so be sure to sample some for a taste experience that is out of this world. Alternatively, try to track down some space yoghurt (宇宙を旅したヨーグルト Uchū wo tabi shita yōguruto, lit. "The yogurt that travelled in space") , prepared from the same yeast.