In Pokémon Platinum, maps 23Eh-247h (dec:574-583) are unused and appear to be test maps for the Distortion World. They do not use the special camera angles of the Distortion World as seen in the final releases of the game.
Credits go to SunakazeKun (GermanPokemon on TCRF) for the discovery of these maps, whom documented these and other maps here: https://tcrf.net/Pok%C3%A9mon_Platinu...
I used save states in DeSmuME to make things easier. To access the maps, I used Pokesav to alter the map coordinates in the save file.