Take a 4-hour snorkeling boat tour to all three islands

Bike around the full perimeter of any island (Gili T takes about 1.5 hours)

Visit the underwater statues off Gili Meno for snorkeling or diving

Get PADI Open Water certified (around $300–350 for a 3-day course)

Snorkel with sea turtles right off the beach (gear rental IDR 25,000/day)