The Jungle trail, is in the National Register of Historic places, http://www.nationalregisterofhistoricplaces.com/FL/Indian+River/state.html
and it's a nice place to go bike riding. We have only ridden our bikes along the 5 mile or so loop, from the VB resort, and they give you a map because you have to ride outh on A1A to the beginning of the trail. Then, we've always headed back when we got to state route 510, but the Jungle Trail continues across that highway, and I think it goes up to the Sebastian Inlet. I know that when we rode our car to the Archie Carr Wildlife refuge near Sebastian, we did come across the Jungle trail there.
The jungle trail is about 4 miles on a dirt path. The return trip is on a macadam sidewalk. The bad part is you can not ride your bike on the path in the park to see the wildlife. Bikes are prohibited.