The waterfall where Sawyer and Kate took a dip and found the gun case (“Whatever the Case May Be,” Ep. 1×12) was part of Waimea Valley, formerly the Waimea Valley Audubon Center (59-864 Kamehameha Highway). Nikki and Paolo later visited the same spot (“Expose,” Ep. 3×14).
Map: 21.6374, -158.0574
Image copyright ABC Studios. Courtesy Lost-Media.com.