Take bus route 24, 12 or 17 to the Vizcaya Gardens Metrorail Station, cross Route 1 using the overpass and walk to South Miami Avenue. From there, head north until you reach the Rickenbacher Causeway (there will also be a large sign for Key Biscayne-you can't miss it). Cross the bridge to Virginia Key (the only hill in Miami!), then follow the path under the palm trees to Crandon Park and Key Biscayne. Starting at S. Miami Ave. and continuing until you reach the galf course this route is 10 miles out and back. It can be extended to 15 miles if you go all the way to the Cape Florida Lighthouse.