Eleuthera is 180 km long and there is no real public transport. A rental car is essentially required — the Queen's Highway runs the full length of the island and most settlements lie on or near it. Roads are generally narrow and patchy; clearance is useful for sandy side-tracks to the remoter beaches.
On Harbour Island and Spanish Wells, golf carts replace cars and are widely available for hire. Water taxis run between North Eleuthera (Three Island Dock) and both islands. Taxis on Eleuthera itself are expensive and best arranged in advance through your hotel.