Answer:
Columbus believed that he had landed in an island somewhere close to East Asia, to China and Japan. This is because the idea behind Columbus voyages was to find a new sea route from Europe to Asia, not to discover a new land.
He actually landed in the Bahamas, likely in a small island named Watling island. In later trips, he landed in Hispaniola, which he thought was Japan, and in Cuba, which he though was part of mainland China. He died without having realized that he had landed in another continent: the Americas.