Taxis are expensive on Savai'i, so be sure to settle the price before setting out.
The easiest and safest way to get around is on an organized sightseeing tour conducted by retired geologist Warren Jopling from the Safua Hotel.
Warren has achieved a measure of notoriety from descriptions in the mass-market Australian guidebooks, which, depending on his mood, he finds complimentary or an annoyance. He does very informative trips north across the lava fields and southwest to the Taga blowholes, but only if four or five people sign up. The cost includes lunch and custom fees. If only two people sign up, it could cost more.
Dive Savai'i at Fagamalo does full-day circle island tours.