One of the strangest weapons deployed by Z'pl'rt the Mad
Admirals, I present to you the future of space warfare! No longer will you need to waste billions of credits on costly space battles, and millions of lives on planetary warfare with hostile cultures. For only a fraction of the cost of a heavy cruiser, I present you with a weapon capable of eliminating an entire solar system. "I present the Star Hammer!"
(A powerful and deviously simple weapon to make space warfare in any sci-fi game forever changed)
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.