Rangeline has a nice setup, too. There's some pretty advanced stuff there, but the beginner loop is the "core" of the trail system, and everything builds off of it. As far as beginner trails go, however, it's a pretty challenging one for Indiana.
Camp Glenn at Ft. Harrison is about as easy as it gets, with the Mann Loop at Southwestway being close to it (it's wider and less technical, I would argue, but it has more elevation change than Camp Glenn does by far).