Some places I'm familiar with -
Hand of Man at his best:
1) Bok Tower Gardens in Lake Wales - beautiful setting on highest point in Florida peninsula
2) Leu Botanical Gardens in near Winter Park - formal & informal gardens
3) Frank Lloyd Wright buildings at Florida Southern College in Lakeland
1) Blue Spring State Park, Orange City
2) De Leon Springs State Park, Deleon
Also check out Clyde Butcher's Living Waters-Aqautic Preserves of Florida that includes nearby natural places to visit.