I would like to know where the houses that were used are located, especially the large, white, cubist looking house with the Art Deco interior decorations.

Most of the houses and other locations used are listed historically on (the website I can't remember, sorry), and they travelled to location for Death on the Nile, Murder in Mesopotamia etc., but for Poirot's apartment building, Whitehaven Mansions, they used Florin Court in Charterhouse Square, London EC1. It's still there today too, as wewe can see in the video. If wewe want a zaidi detailed idea of the location, check out HerculePoirotCentral for maps.

link

Hope this is what wewe wanted! If wewe want zaidi information, just leave another swali and I can probably help you. :)