It sounds like you got banged up pretty badly. What you are basically describing is premises liability.
The nuances vary by state, but generally, when someone is on your premises who is not trespassing and who is not there for your commercial benefit, you are liable for injuries sustained by anyone as a result of an unsafe condition. Under these conditions, for this duty to exist, (1) the owner must either know or should know of the hazardous condition, (2) should have realized that it involved an unreasonable risk of harm to the visitor, (3) and should have expected that the visitor would not discover or realize the danger; (4) the owner must have failed to exercise reasonable care to make the condition safe, or to warn the visitor of the condition and the risk involved; and (5) the visitor must not have known or had reason to know of the unsafe condition and the risk involved.
So ask yourself: (1) should the owner have known about the hole? (2) should (s)he have realized that it involved an unreasonable risk of harm? [is it reasonable to have these sorts of conditions, given the danger?] (3) should (s) have expected someone would not realize the condition or danger? [think about how many people pass by there--sooner or later, is someone going to fall in?] (4) did the owner warn of the danger? (5) did you have reason to believe the hole was there?
I have not seen the premises, so I am not in a position to answer these questions---but it seems to me that there was a dangerous hole, the property owner had the duty to fix the hole, you fell in as a result of the unfixed hole, and you were injured as a result of the unfixed hole. Sounds like a case to me.
I would recommend that you speak with an attorney that handles slip-and-fall cases rather than contacting the property owner directly... the property owner isn't going to want their insurance rates to go up and the insurance company isn't going to want to pay out; they will be looking for ways to get out of it.
The question then is how to document what happened. Keep records of all of your medical bills and treatment, take photos of the accident scene, and get contact information for any known witnesses.
I would take your case if you walked in my office door. I wouldn't encourage anyone to take advantage of the system, but speaking with an attorney will make sure that your rights are protected. Best of luck.
If this was informative, please click "accept" so I may receive credit for my personal time and knowledge. Thank you.