Unlike the person who inspired me to post this, I'm ruling out actual magic (or equivalent technology). So, there is going to be some financial cost associated with the place, the amount of space available is going to obey the normal laws of physics, there is no teleporter conveniently stashed in the garage, it doesn't clean itself effortlessly.
A big house, 7 or 8 bedrooms sort of thing, pre-1930s with a bit of character, though modernized and easy to run. If I have to pick a location I'm thinking north Oxford somewhere; Oxford's a good place to live on its own merits and also sensibly accessible from London.
Inhabited by a group of loosely connected friends living there. Not a commune in the hippy / organic / grow-your-own vegetables sense, but a structure more closely connected than just co-tenants in the same physical building, but less closely connected than a traditional nuclear family.
Everybody has their own room, and other members of the household don't drop in without invitation. There's at least one guest room and plenty of sofabeds and other facilities for visitors to stay over. There's a decent size communal living room where people can hang out together without being all cliquey shut in their rooms. (Though of course, people can invite others to their room if they do want to socialize in a more one-on-one and less free-for-all way.) It's big enough for parties but mostly it's just space to go if you want to be sociable. If there are TVs, hifis etc they are in people's rooms and not in communal areas.
The rooms are as soundproof as physically possible. Ideally I'd like to be able to go into my room and close the door and play loud music or have sex or an argument without annoying the rest of the house. But I'm trying to stay with vaguely realistic here, so let's just say decent soundproofing.
The kitchen takes up the whole basement, old-fashioned in layout but with modern amenities. A flagstone floor would be cool, and a big ceiling beam with hooks in it. It's an eating place as well as a cooking place, with a big dining table in it. Any kitchen equipment used for meat is kept separate and clearly identifiable (this works for kashrut and vegetarian both, I hope). Gas cooker. A huge cabinet freezers and at least two double-height fridges. Plenty of working surfaces and plenty of cupboards, at least some of them within reach of short people.
There are excessively many bathrooms. Depending just how realistic I'm being, either every room has an en suite bathroom, or at least no more than 2 or 3 people are sharing. There's a toilet that's not in any of the bathrooms. Unlimited amounts of instantly available hot water; in my real flat this happens by means of a combi boiler, but there might be more efficient ways of doing it.
There's a garage used for storage. If there are cars involved there's on-street parking, but cars don't figure very highly in my daydreams. There might be an attic too, cos attics are cool. It goes without saying that the house is geek-compliant; it would have wireless broadband at the least, and hopefully its own server assuming someone (not me!) was competent to sysadmin it.
Housework is shared out fairly because everybody feels a commitment to keeping the place pleasant. Which doesn't necessarily mean that everybody takes turns to do everything; people contribute as best they can, and unpleasant chores can be switched for not so bad ones with people who have different views on these matters. You're allowed to pay someone (a professional cleaner, not a housemate) to do some of your share, if you feel like it and can afford it. This doesn't mean endless meetings to negotiate exactly how the housework should be divvied up, because if there's one thing more boring than housework it's meetings about housework. I'm starting from the assumption that the people living in this house are the kind of people I trust to be generally decent and pull their weight anyway, otherwise I wouldn't want to form a household with them.
The default assumption is that people buy their own food and explicit permission is required to borrow from a co-householder. But people are free to make individual arrangements, such as a pair or three people deciding to pool shopping, cooking and eating resources. Basic household supplies (toilet paper, cleaning things etc) are in common. I'd think an arrangement like everybody contributing a certain amount each month to a pot; the actual shopping counts as one of the household tasks.
Partners are either part of the household, or they are live-out partners who may visit occasionally but not stay more than a couple of nights on any regular basis. There are no partners who just coincidentally happen to find themselves spending most of their time in the house, but don't have any financial or emotional stake in the household. The household may agree to take in a friend who really needs somewhere to stay, on an 'until they get their life sorted out' kind of basis, but it would have to be by general agreement. And good friends or partners who live a long way away can stay for a couple of weeks as a one-off thing, just as long as they don't move in.
There are no animals, or possibly there are cats, but I'm leaning towards no animals. If there are children, they are outnumbered at least 3:1 by adults. Responsibility for the children is considered one of the household tasks; some people may lean more towards childcare and less towards keeping the houseclean and vice versa. As far as is reasonable taking into account their age, the children count as members of the household, with responsibilities for housework and a say in decisions that need to be taken. The children's actual parents have the final say in things like discipline, but active involvement with them goes with being a member of the household.
Yes, I am actually describing a fantasy lifestyle which involves children! I still have no intention of having any of my own, but I can see myself living with parents and doing my bit to help with the kids, as long as I had at least a couple of other adults equally committed. And the chance to live with good friends would outweigh the inconvenience of having children around. I don't want to insist that the house should be a completely childfree environment, cos that would rule out some of the people I have in mind I want to live with, plus some hypothetical people who might also make good housemates.
I don't know if this is at all realistic, but I'd hope for some kind of financial arrangement that makes it possible for people to leave without huge financial penalties either on them or on the rest of the household. The way I think it might work (assuming that I somehow had a windfall of a substantial amount of money - being unlimitedly rich counts as magic, but a defined lump sum is just about plausible) is if I were to own the house, and the other householders would pay rent to me on the basis that they would become part-owners in proportion to how much they'd payed. I haven't quite figured out the details of this, but anyway. It would also be a bit more comfortable than having my friends be my tenants in the conventional sense.
OK, so it's basically a student house with frills. What can I say? I never asked to grow up!
Today is the 24th day, making 3 weeks and 3 days of the Omer.