Toledo Metroparks' massive Oak Openings Metropark. Lupine, at least this species, grows best in dry sandy substrates. The Oak Openings has plenty of sand. This elliptically shaped region encompasses the old beaches and dunes of pre-glacial Lake Erie, dating from a time when the lake sprawled much further inland than it currently does.
Lupine is a rarity in Ohio, and nearly all populations occur within the Oak Openings. Hit the right spot, and there can be a lotta lupine, creating spectacular blue clumps and besting any ornamental plant in the looks department. If you are a seeker of rare flora, there will be plenty of other goodies to find. The Oak Openings and its unusual habitats harbor probably the greatest number of rare plant species of any place in Ohio, of similar size.
Should chance permit, I'd highly recommend a visit to the Oak Openings next May. The aforementioned Kitty Todd Preserve and Oak Openings Metropark are must-see destinations. Take a camera.