I ride the Tammany Trace. The whole thing is paved, but a bridge is out near the east end, and the easiest way around is riding a gravel shoulder, unless you're into riding narrow, fast moving 2-lane highways. I'd take a road bike and avoid the area where the bridge is out, or take a cross bike/hybrid and ride around it.

There's great dining, a really nice brewpub, a bed and breakfast, a great lakefront area, a small kid's waterpark, a playground, and lots of parking. The rangers are super friendly. I go as often as I can. Most of the time, I'm riding with a 700x23c. My half century was done on 26x1.95 knobbies, which made short work of the gravel.