This is the labyrinth at the back of the sculpture garden at the Delaware Art Museum. There is no sign leading you to it, but it's easy to find if you know where to look.
It's immense. The top photo shows how it looks from outside, the other is the interior view. It consists of an immense pit, surrounded by a wall faced with large, irregular stones. It puts you in mind of one of the ruins you find in Rome. These pictures don't do it justice, it looks ancient and timeless. And very hushed. You have the illusion of being in some isolated rural spot, miles from anywhere.
There are a couple of rustic seats in the labyrinth, and I sat in one of them and savored the silence for a while.