An ordinary trespasser is defined as anyone coming onto the land without the express or implied permission of the land occupier or without a legal privilege to enter the land. There is no duty owed to a trespasser whose presence on the land is unknown to the land occupier. Further, the land occupier is under no duty to discover the presence of the trespasser. This is true with respect to both natural (e.g., a hidden bog) and artificial conditions (e.g., an excavation pit) existing on the land as well as in regard to all activities occurring on the land.
However, if the land occupier knows or should reasonably realize that there is a trespasser on the land, he is under a duty to exercise care to either warn the trespasser of, or make safe, artificial conditions or activities that involve a risk of death or serious bodily harm.