My family and I all met in Milwaukee for my cousin's graduation, and we went to "The Domes," or the Mitchell Park Conservatory, which is part of the Milwaukee County Parks System.
There are three domes:
3. The Floral Show Dome
Each dome is 1 Acre underneath and has full of an assortment of plants appropriate to the climate of the dome. Admission is only $6.50 for adults, and Senior Citizens, people with disabilities, students, and children all get in for $5.00. It is definitely a unique experience if you ever visit Milwaukee.