If you need to refresh yourself, make a beeline for Kwaibala Waterfall, about 3km from Auki. This little waterfall drops into a few pools that beg swimming. It's a 30-minute walk from town, or you can take a taxi (S$20) then walk the final stretch (about 20 minutes) along the Kwaibala River to the waterfall.
It's not signposted; you'll need a guide to get there.