Oktokki Space Center is a family-oriented aerospace science park on Ganghwa Island, with exhibits and activities built around rockets, space travel, and basic science. It is aimed more at children than specialist aviation fans, but it makes a useful rainy-day or family stop if you are exploring Incheon's outer islands.
The centre works best as part of a wider Ganghwa trip rather than a reason to cross the city by itself. Pair it with Jeondeungsa or the island's historic sites if you want a fuller day.