Nail Board is an ominous world accessible through Kubotsuki's Nexus.
Features
This world features decrepit planks of wood with nails screwed into them, floating in some sort of void. Northeast from the entrance is a very long plank with a stack of orange blocks at the end. Interacting with this will take you to the Alphabet Tower. Continuing on the path downward from the entrance, you will eventually come across a large hammer. Directly north of the hammer is a post with a cloth tied around it which brings you to the Red & Blue Passage upon interaction.
Directions
Kubotsuki's Nexus → Nail Board
Gallery
Entrance to Alphabet Tower
Entrance to Red & Blue Passage