"Have you ever felt like there’s a world just beyond ours? Some sort of strange dimension, a light dancing just beyond our fingertips? Well, I’ve touched that ‘sacred’ world, and I know its true face."
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.