What city is 18 degrees south and 175 degrees east?

There's no city there. That point is at sea in the Pacific Ocean, about 150 miles

west of Viti-Levu ... the "big island" of Fiji.

City-wise ... The capital of Fiji at Suva is about 225 miles to the east of that point,

Port-Vila, the capital of the Vanuatu group, is about 440 miles west, Brisbane, Australia

is about 1,440 miles southwest, and Honolulu is about 3,300 miles northeast.