The invention that greatly improved navigation in the 15th century was the magnetic compass. It allowed sailors to determine their direction even when the sun and stars were not visible, marking a critical advancement in maritime exploration. This led to more reliable sea voyages, facilitating the Age of Discovery. Innovations like the caravel ship design also emerged during this period, allowing for longer and more daring explorations. The combination of these advancements significantly expanded European interests in trade, colonization, and the understanding of the world's geography.