I always liked the idea of an exploration CTB. Go on an expedition somewhere extremely dangerous for whatever reason and explore until whatever ends you.
Maybe studying grizzly bears in Alaska, polar bears in the arctic, exploring the upper Amazon in Ecuador, so many options!
You won't get wifi or Starbucks out there, but you might find a unique way to CTB. The only downside is you can't control the time or method of CTB, so you might end up with something that takes days of agony to CTB, or something really fast and unexpected. It's a random game.