If you’re looking for something less structured than a conservatory, but more walkable than a forest, the Morton Arboretum is for you. It’s in Lisle, which, from where I live (Little Village, southwest of the Loop) is about a 1/2 hour drive during non-peak hours.
It’s early spring still, so the staff chagrinedly admits there is not a whole lot to see until late spring, summer, and fall, but there are still beautiful pines and tiny little budding flowers, ready to cast off their casings and rock out hard. No matter the season, too, the landscaping is still stand-out, and also makes a great background for costumed photoshoots.
My neighbor, the performance artist, can often be seen out and about as a pug or dinosaur (“It motivates me to get in shape and go out jogging, it’s just more fun that way,” she says.)
You’ll probably go as yourself, but if you feel like putting a costume on, you’ll get no hard looks at all, and get a mostly buoyant reception from all… but DON’T CLIMB THE TREES (she learned this the hard way.)