COSI is one of the best science museums in the Midwest and one of the few things in Columbus that legitimately justifies a special trip. The exhibits are genuinely interactive — you can walk across a high wire on a special balance bicycle, explore a recreated ocean, and handle real moon rocks. The space exhibit and the life sciences wing are highlights; the energy exhibit has enough hands-on machinery to keep adults engaged as long as kids.
The building sits on the west bank of the Scioto River, connected to downtown by a pedestrian bridge. Even if you skip the museum, the Scioto Mile riverfront path alongside it is worth a walk. Plan at least three hours if you go in; COSI is large and easy to underestimate.