Just up the path from the Pond, or down the path from the ROF Bunker. A good view of one of the ponds from the hump of overgrown Earth bunker entrance. From the left hand entrance, cross over the railway lines, turn left and head to the daylight. There is an opening which leads to a dark, dark alley way, don't take it cache is near by. Don't ask me what was made here, I just don't know.