Review of The Drifting Classroom (1972)
Umezu Kazuo (writer-artist).
To me, this is an iconic example of a classic motif in horror and weird fiction: The unaccountable transition from safety in a familiar and realistic setting into a nightmare: A change so profound that, unlike in The Fur Country (1872), return is impossible. Umezu’s medium and juvenile style are just right for this motif, better than, for instance The Narrative of Arthur Gordon Pym of Nantucket (1838).
References here: Time Trap (2017).