Located in historic, trendy downtown Coconut Grove, Barnacle State Historic Site is well worth your time. Park nearby in public parking ($12/day) and you'll also be set for browsing shops and restaurants in the downtown area.
Built in 1891 by Commodore Ralph Monroe, the Barnacle House is the oldest house in its original location in Miami-Dade County. Walk down a beautiful shaded lane, through one of the last remaining tropical hardwood hammocks, past a carriage house, and you'll arrive at the custom-built house, which still contains most of the family furnishings.
This five-acre property also features "the cave," a mysterious, hand-dug pit cut right of of limestone, and a boat house Monroe used to design, build and repair various craft he sailed in Biscayne Bay. (During his lifetime, he designed 56 yachts.)
Bring cash to the site; admission is on the honor system and is a paltry $2 that you place in a state park envelope and drop in a metal box. Touring the inside of the house costs $3 and is well worth it; pay at the house. Tours only run 4x a day, so mind the schedule.
For a mere $5, you get a terrific stop with great atmosphere, an insightful look into a long-forgotten past, and a charming introduction to one of south Florida's most interesting pioneers.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.