“The Last Broadcast #1” is brought to you by Boom! Studios’ Archaia line and lives up to its promise of being “an urban exploration adventure.” Spelunking has been the subject of comics before, believe it or not. That goes back to 2009 and Jeff Parker and Steve Lieber’s “Underground.” That comic is a character-driven action adventure, which is saying a lot. Either you’re one or the other most of the time. Well, lightning strikes twice with “The Last Broadcast.” And all of the action is not just underground.