Board Thread:General Discussion/@comment-27907368-20160412010659/@comment-28069050-20160418175010

OK, I found this myself.

In the Ruins, the third room with switches, walk to the left of the pillar nearest to the exit to the next room. Press Z. You'll fall into an empty room, and when you get out, you are transported to the first room with the switches. I have a theory that if you return here after a True Pacifist Route, you'll find some monsters. Haven't confirmed this theory though.