Physically search the site as thoroughly as you can. Take your time and have a good look around, preferably with a camera and take as many photos as you can.
They are a great help later, but take them in some order North to South, left to right or both. Just make sure they make sense before you come away from the site.
Are there any old, buried buildings, like air raid shelters or pillboxes from the last war? These can be extremely well built and cost a great deal of money to remove. Unless of course, we can turn it into something useful like a pond….
Likewise, check any existing old buildings for basements. If they’re not needed, we would need to fill them in. Check also for old foundations which might need removing.