Koroyanitu National Heritage Park is accessed via Abaca (Am-ba-tha) village, southeast of Lautoka, but you can't go alone: trails have been unmaintained for years. Contact Kalo Baravilala, who can arrange everything from guides to accommodation.
From here, it's possible to make a day trek to and from Fiji’s sleeping giant, Mt Batilamu. This is a strenuous three-hour hike up, and a knee-wobbling couple of hours down. At the time of research, it was not possible to walk the two-day trek between Abaca and Navilawa villages.
You can overnight at Abaca’s simple Nase Lodge ($45).