Krohn Conservatory is Cincinnati's grand public greenhouse, set in Eden Park near the Cincinnati Art Museum. Inside are tropical plants, desert species, orchids, palms, and seasonal floral displays, all under glass and close enough to downtown to work as an easy hour-long stop.
It is especially useful in winter or bad weather, when the warm, humid rooms feel like a small escape from the city outside. Combine it with the art museum and the Eden Park overlooks for a compact east-side itinerary.