Boerner Botanical Gardens are located just outside of Milwaukee. Though smaller than other area gardens, they are full of interesting plantings. Additionally, they have a large water-feature area (off when we visited pre-season). There is also a large play area for children and a very attractive visitors center. Be sure to check times and dates before you visit.

Boerner Botanical Gardens
9400 Boerner Drive
Hales Corners, WI 53130