Ral - Reverse lightning bug

          Where the stone tower ended, the stairs emerged onto a flat deck that formed the base of a broad copper dome. The machinery of the beacon was concentrated in the center of the room, arrayed around a single vast resonating crystal. That was the heart of the thing, the technology Ral had salvaged from Project Lightning Bug, vastly scaled up and inverted. When the proper current was applied, it would become a blazing torch, shining forth into the Multiverse. At least in theory, every Planeswalker would be able to see it, and find their way to Ravnica.

***

The Gathering Storm, Chapter 19