sometimes its done in order to avoid spoiling the external look.
Ive built windows especially for this purpose on period properties.
Its funny how people often dont even notice it -Ive even known people buy a house and not notice until they move in.....
*Thinks* The fake houses at Leinster Gardens that hide the tube line.
https://www.citymetric.com/transpor...-reveal-how-london-underground-used-work-3448