Wailoaloa is the long, dark-sand beach about ten minutes west of Nadi town, lined with budget backpacker hostels and a few mid-range resorts. The sand is volcanic-grey rather than the postcard white you came to Fiji for, and the water can be cloudy when the river is running — but the sunsets over the Mamanuca Islands offshore are spectacular, and the beach bars catch the breeze.
It is the cheap, lively alternative to Denarau: easy to walk between hostels, friendly, with kayak rentals and horse rides along the sand. Don't expect to swim seriously — Fiji's good beaches are out on the islands, not here. Come for the cheap dinners, the sunset Kava sessions, and the easy ride to the airport.