GMs definitely need to enforce strict "in character" play, eliminate "across the table" chatter, and by doing so - set the scene for an awesome role-play experience!
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.