There was once a tribe of humans that was referred to as “the Wild Ones.” They were humans who were linked to the wild natural world, having animal characteristics.
This man looks like no one to be trifled with, and that assessment is correct.
You come upon a ruined building in the back section of a city park (or other out of the way area of the city). The ruins are fairly overgrown. All that is really standing is a doorway and its frame. If you pass through the opened door, you travel to a different world. If the door closes, there may not be a doorway back to get you back.