Shikoku (四国) is often dismissed as a rural backwater with few must-see attractions, but a visit can wash away those doubts — and leave you with a glimpse of the elusive "Real Japan".
The name of the island literally means "four countries"; indeed, Shikoku consists of four ancient countries (now prefectures), whose original names are still found in traces: Ehime (Iyo), Kagawa (Sanuki), Kochi (Tosa), and Tokushima (Awa).
Shikoku is far enough off the beaten track that some Japanese ability, while not absolutely necessary, will come in handy. Some dialects, notably Tosa-ben (spoken in Kochi), are famously incomprehensible even to other Japanese.
If you're coming from Hiroshima, ferries from Ujina to Matsuyama are the most direct route to Shikoku. However, if you're skipping Chugoku entirely, buses from Kobe cross the Akashi Kaikyo Bridge (明石海峡大橋) over Awaji Island (淡路島 Awajishima) on their way to Naruto, close to Tokushima. There are also ferries to Matsuyama from several cities in Kyushu.
Shikoku is not connected to the Shinkansen network, but there are frequent rail connections from Okayama to Takamatsu, and from there throughout the island. The limited express Shiokaze (特急 しおかぜ) runs back and forth between Okayama and Matsuyama roughly every hour during the day.
The Japan Rail Pass  will cover travel on JR lines throughout Shikoku by the same rules as the mainland. However, for travel exclusively on Shikoku, JR offers the Shikoku Free Kippu (四国フリーきっぷ) , which allows unlimited usage of JR trains and buses, including limited expresses, on three consecutive days (¥15,700). If you manage to time it so that you can start on your birthday, ask for the Birthday Kippu instead, and you'll get the same deal for just ¥10,000!
For the frugal traveler, the Shikoku Saihakken Haya-Toku Kippu (四国再発見早トクきっぷ )  may be a better deal, as it offers one day of unlimited travel for just ¥2000. There are three big catches though: it's only valid on weekends and public holidays, it's limited to local trains, and you have to buy it at least one day in advance.
Buses fill in the gaps in the train network and are the only means of transport in areas like Cape Ashizuri and the Iya Valley. Schedules are sparse and prices are high. Some parts of the JR network, notably the southern segment from Kubokawa to Sukumo, have been split off to the private Tosa Kuroshio Railway company.
The pace on Shikoku being what it is, don't plan to go anywhere in a hurry. Train information is likely to be in Japanese only, unlike what you may be used to from the Shinkansen, so either brush up on terms such as "unreserved seats" and learn to recognize the names of the places you're planning to visit in kanji, or get comfortable chatting with strangers.