This is Codorus State Park and the Mary Ann Furnace Trail
I have walked the trail several times over the past several years. By my Garmin GPS, it appears to be a about 2.1 miles. It is hilly in spots. Some of the trail runs right along Lake Marburg, Other parts move to higher country. Some areas you can take a slight detour down to the lake and back. There is parking at Black Rock Road. There is also plenty of opportunity to see wildlife along the way. Here is more information from Pat Carroll. Here is my earlier post on this trail.