Expedition cruises have exploded in popularity over the past decade -- and for good reason. They allow travelers to access some of the most remote, fragile, and breathtaking corners of the world: Antarctica, the Galápagos, Arctic Svalbard, the fjords of Patagonia. But with more ships, itineraries, and operators than ever, how do you choose the right expedition cruise for your style, your schedule, and your sense of adventure?