One shared house I lived in had timed light switches in the hallway: the big round ones that would only stay on for a minute or so.
@Caspianberg I love the old cellar, only accessible from outside. I want one like that! In one flat I lived in, I kept the freezer on the (very enclosed and sheltered) balcony, to save space in the kitchen. I also had a tiny tabletop dishwasher, as sometimes seen in office kitchens.
There was one feature I thought of building in the same flat, which would have been very unusual. The entrance hall was always very dark: I thought of building an internal window in the bathroom wall, facing into the kitchen, which would let light through the bathroom into the hallway, with a blind in the bathroom that could be lowered for privacy: I'd seen a similar internal window in a house to make an internal staircase lighter. I never had it done; I'd probably have had to block it up before selling! I suppose that more realistically, I should have installed a front door with windows in it.
In my present house (1930s semi), there was a gap in the wall between our attic and the one next door; we could look through and see into their attic, which was quite empty. We had this gap bricked up.