You can get a good idea of the size and shape from terraserver. Located just north of the southernmost bridge connecting to I-91 over the Ct river.

The out buildings and perimeter are easily accessed. I have never been challenged, but I pick my days.

The iron portcullis is actually a swinging gate with a rotting wooden swing gate behind it. A railroad spur runs up to the exterior courtyard by the Iron gate. The north interior courtyard is full of trash, old desks and the leavings of the many homeless in Springfield. Bring a friend.