Our cat is a house cat. She has a run that is attached to the utility room so she can get our door access, but in safety. She is harness trained and is quite content to come out for a walk with the dog. I also take her out in the garden where i potter and she has an explore, munch of grass and a climb of the trees.
She is an indoor cat for a number of reasons. She's an unusual looking cat and would be lifted [a number of cats from our village have been stolen], she'll not get run over [have had one cat that that has happened to], there have also been a number of cats poisoned by anti freeze in our estate.
------------- My photos allow you to see what I saw at the time that I took it....No messing.
I've known several folk with indoor upper floor flat cats. One let the cat go out onto the 3rd floor window sill - I've seen cages attached outside window frames for this, which stop the cat leaping out. My own cat used to get out of an open top light if he felt like going out, and safely jump off the first floor window sill. However, I know a girl who got a kitten; she was out at work all day, the cat was indoors all day, and the (male) cat eventually decided it was top cat, and that she was an intruder in its territory - it attacked her when she was asleep in bed. Sounds bizarre, but it's true. She rehomed the cat to a farm with 3 dogs, and the cat now happily knows its place.
In the past, I've had outdoor and indoor cats. It's a difficult decision, but here's my experience.
My outdoor cats were moggies and loved going out and loafing around my garden. When they came in, they were loving and affectionate. Unfortunately, both of them succumbed to car accidents (not at the same time). But they were happy wee cats.
My two indoor cats were a Maine Coon and a Ragdoll. I was advised to keep them as indoor cats and it was a complete disaster. They were miserable and aggressive. They both paced up and down my window cills and it was awful to watch. My Raggie took any opportunity to escape, even cutting his mouth on the window to try to open it. The Maine Coon just became aggressive and in the end, both had to be rehomed. I took loads of time to do that and would you believe, they both went to homes in the countryside, where they could get out more safely.
I honestly don't think cats should be kept indoors. Their instincts are to go out and hunt and stalk. I'll never do it again. However I can tell you that if you keep a kitten inside till it's 6 months, there's far less chance of it wandering that far.