“This is a really random tidbit, but Moonrise Towers used to be two towers,” Vincke explained. “And now, we shipped with only one tower. And for a long time, there was actually the ruins of the second tower, and then we removed that also.

I was wondering about this all through that part of the game. I scoured every path I could figure out how to reach, inside and out, but ultimately found no second tower. Welp, that explains it.