Viti Levu - is the main island of Fiji. There is an international airport, as well as the largest cities in the country. Island beaches are not very good, but there are many interesting attractions, - Sigatoka Sand Dunes, Navua river with beautiful canyons and many more. Shore and seabed: rocks, sand. 
Local hotels are generally cheaper than those at small remote islands, but still overpriced. Good news is that you won't be forced to take hotel's full board meal plan, like they love to do in most of the Yasawa Islands.