Before a plaintiff may recover for damages allegedly caused by another's negligence, the plaintiff must establish a legal duty owed the plaintiff by the wrongdoer. Ries v. Steffensmeier, 570 N.W.2d 111, 114 (Iowa 1997). The existence of a duty is a question of law for the court to determine. Fry v. Mount, 554 N.W.2d 263, 265 (Iowa 1996). Restatement (Second) of Torts states the general rule applicable to the liability of possessors of land for injuries caused by conditions on the land: A possessor of land is subject to liability for physical harm caused to his invitees by a condition on the land if, but only if, he (a) knows or by the exercise of reasonable care would discover the condition, and should realize that it involves an unreasonable risk of harm to such invitees, and (b) should expect that they will not discover or realize the danger, or will fail to protect themselves against it, and (c) fails to exercise reasonable care to protect them against the danger. Restatement (Second) of Torts 343, at 215-16 (1965).