One of the most popular atolls to visit, Arno is reachable by a 45-minute boat ride from Majuro. It offers white-sand beaches and waters with plenty of marine life—including sharks. There’s a simple cabin to rent for overnight stays and a tiny snack shop (it’s a good idea to bring your own food and water, as well as mosquito repellent). If you’re lucky (or ask nicely), the friendly locals may make you some coconut crab.