Give a cat a whole house and it will spend most of the day on the one narrow ledge by the glass. That isn't a quirk. It's three needs being met at once, and understanding them tells you a lot about what an indoor cat is missing.
1. Height is safety
A cat on a high surface can see what's coming and can't be approached from above. In a house with a dog, a toddler, or simply a lot of footsteps, elevation is where a cat relaxes. Floor level is where it stays alert.
This is why a nervous cat in a new home heads for the top of the wardrobe, and why adding vertical space often calms a household more than adding floor space.
2. Warmth
A cat's comfortable temperature is several degrees above ours — around 30–38°C. That's why they find the sunbeam, the radiator, the laptop. A sunlit window is the warmest spot in most rooms for most of the day.
3. The window is television
Birds, people, weather, next door's cat. For an animal built to watch small moving things for hours, a window is genuine mental stimulation — and it's the only stimulation an indoor cat gets that changes on its own.
The problem with an actual windowsill
Most are narrow, hard, and often have a radiator underneath that makes them too hot in winter. Your cat uses it anyway, badly, and wakes up stiff.
A hammock that mounts on the glass gives the same three things properly: it's wide enough to stretch out, it's in the light, and it takes no floor space at all — which matters in a flat where a cat tree simply doesn't fit.
If your cat is at the window all day and restless at night
That's a cat with enough watching and not enough doing. The view provides interest, not exercise. Ten minutes of real play before your last meal of the day is what turns the nocturnal pacing off — more on why they wake you at 4am.
One safety note
Cats fall out of open windows more often than people expect — it has a name, high-rise syndrome. A cat asleep in the sun can slip while stretching. If your windows open and you're above ground level, screens are not optional.