If the artificial lighting is good, or even better - well-designed, and you have good ventilation/extraction then the bathroom can be a nice space. Windows are good in bathrooms but it is the most private space so windows usually have to be obscure which defeats their point. Windows also make the space colder so there is a line of thought that would even suggest against windows in bathrooms. good luck

www.dorarch.com

It's the ventilation which worries me most.

Ventilation is the main issue. We previously lived in an apartment that had an ineffective ventilation system rather than an extraction fan, as the bathroom didn't back any external walls. Biggest issue was mould on the ceiling and moisture escaping to the adjoining rooms after a shower.

If there is no other option I would invest in a really powerful humidistat extractor fan (150mm rather than the smaller 100mm openings) that overruns after the light is switched off.

I have lived in a couple of houses with no window and it has never bothered me or family

Nearly 18 months now with an internal bathroom. The Vent-Axia Svara extractor fan was well worth the money. Runs 24/7 at low speed and then increases whenever it senses the light being switched on (it doesn’t interact with the light circuit) or humidity level increases. Bluetooth connection to your phone means easy to get the settings right. Definitely worth the extra £60-80 versus a normal extractor. Not a spot of mould - yet. I bought a second one for downstairs WC.

I am convinced this plus opening windows a crack has improved the ventilation for the whole house - no longer any condensation on the single glass Victorian sash windows.

Internal walls in an internal bathroom mean the walls are warmer, so less condensation and thus less mould versus our previous bathroom - which was surrounded on the outside by 3 solid cold walls and 1 ceiling.