Key Biscayne is an island connected to the southern part of Miami, connected by the Rickenbacker Causeway. There are three especially nice runs in this area.
Rickenbacker Causeway Path. The 3.1 mile path from the foot of the bridge in Miami to the Aquarium is exhilarating, with great water views in every direction. Access the causeway from Brickell Ave. to the north (downtown) or Bayshore Dr. to the south.
Crandon Park is a great area for running in the northern part of Biscayne Bay. Accessed just past the Causeway (or left off the Causeway if you are running/driving), the 808-acre park features as well as a marina, golf course, tennis center, family amusement center, picnic shelters and a nature center. The beach on the Atlantic side is 2 miles long, and there are also miles of trails suitable for running. It’s 2.7 miles from the Aquarium to the end of Crandon Park.
Virginia Key. An 82 acre barrier island right across from the Aquarium. There’s a mile-long beach with great views (but not that runnable). The running highlight is the 4+ miles of trails, very popular with mountain bikers. Runners please respect. Trail info.
It is also possible to put together a long run from Miami to the end of Key Biscayne. View map below.