Traincar

The Traincar (alternatively the Train) is part of the Dense Woods. It is exactly what it sounds like- a lone part of a train, found by following a path where eyes watch you (accessible from Hell).

Once inside, the train begins moving on its own. A red-eyed man is sitting on the bench inside. Sitting next to him and moving Madotsuki's head up and down seems to allow you to progress. Two creatures with large eyes appear inside and the sky changes to purple from blue when the requirements are met.