They actually rebuilt a cabin similar in size and location to the specifications on deeds and some educated guesses. Then to protect it they built a mausoleum around it. It looks a bit absurd considering the simplicity of the man.
It's a small hike from the visitor's center, which has several items from Lincoln's life, a mock up of the inside of a typical frontier cabin, a short film, gift shop, and an information table where you can get the gouge on other local attractions and your map and stamp. The closest Lincoln landmark is Lincoln's Boyhood Home, about a dozen miles away.
The walk from the visitor's center to the cabin.
Downhill from the "cabin" is the well/spring that made the plot of land so valuable. Don't worry, it's pretty well roped off. Kind of neat-o in a cavey way.
As you can tell from the pictures, there are a lot of roped off areas. Due to spring rains, most of the trails were off-limits during our visit, but apparently there are a couple miles' worth of hiking you can do, and the area looks pleasant and shady once the trees have leaves. Maybe next time.
Another feature on site is the historic inn. Back in the days when family road trips were coming in vogue, this "hotel" was built where you could stay in rustic cabins to get the real experience. Now they are their own part of history. You can't stay there anymore, though, but you can get a few snacks.