Draw a 1 mile diameter circle around it, and run a custom search to identify those properties that have sold for cash in the last year.

I would dig a hole about 3' deep and 2' in diameter down there.  

My day job as an engineer is making life saving devices for the medical industry (used to do coronary catheters and stents for people suffering heart attacks, currently working on dialysis access for patients with failing kidneys)The lower wall was concrete and steel reinforced, it was constructed of blocks that key together with 1/2" diameter fiberglass pins so that it doesn't shift while being filled with concrete. 

Old cast iron pipes inside diameters are typically about 1/4 of the original size due to mineral/corrosive build up.

If it's a large diameter well pit (brick or stone lined) you could have a dangerous situation.

Before I knew what he was doing he had punched and kicked holes in the bedroom wall, one more that a foot in diameter. 

It is about 12" diameter.

@Mike Reynolds I build houses using ANSI class 5 pilings with a minimum of 6" diameter tip (which means at 35-40ft long, they are about 12" diameter at the top.  

If it's a round post over 8" in diameter, the paint can stay exposed, just can't be loose or peeling.

There is another brand called Wirsbo or Uponor that uses slightly larger diameter fittings and doesn't have 'crimp' rings.