A property owner must keep his property in a reasonably safe condition. He must discover any unsafe conditions and repair, replace or warn of any condition he could expect to harm others. 

His reasonableness will be measured by the following factors:

• Location of the property
• Likelihood that someone would come on to the property as the victim did
• Likelihood of harm
• Probable seriousness of such harm
• Whether he knew or should have known of the condition that created the risk of harm
• Difficulty of protecting against the risk of such harm
• Extent of his control over the condition that created the risk of harm.

But if the city, state or the federal government owns the property, then the rules are different and getting compensation for an injury is more difficult.