I started my trip to Shikoku at Washuzan Highland, an amusement park built on the side of a hill looking out over the Inland Sea toward Shikoku. The park is actually on Honshu, just a short ways from Okayama. The park is Brazilian-themed, mainly in the daily events and some food options found inside.
Food offerings at the cafeteria are fairly interesting; there's a samba burger with fried meat, a curry naan hot dog, Brazilian pizza on naan, and fresh juices including coconuts in the shell. At the top of the hill, Baiya Cafe has other interesting offerings including tacos, dry curry, cheese balls, and curry naan dogs again. There's also a buffet with American-style dishes that I didn't visit - it looks like access is from outside the park. Prices are reasonable and the food was good, though it wasn't anything I'd go back for. Actually, if I do find myself with time and interest, I could try the buffet for lunch or dinner.
The park isn't very large, so even with the uphill hike one could do the entire park in just an hour or two. But with rerides, the samba show, and the water park, you could make a half-day or more out of your visit. I stayed until about 3 PM without visiting the water park or watching any of the shows. In August, when I visited, it was hot and humid - you have been warned.
Admission with "free pass" for rides is 2800 yen, and the park is generally open 10:00-5:00 with extended hours most weekends and in the summer. From Okayama, Kojima Station is only about 30 minutes away; the park is just five minutes more than that by bus, though it's a good idea to find a schedule to time your transfer properly.