I only had a half-walk today. Just around one block. Because Autumn is a bitch and I neglected to put my inhaler in my long pants. But that doesn't matter so much.
The idea is a little bit Playing Beattie Bow and a little bit Chronicles of Narnia and a lot of steampunk and a dash of solarpunk and some weird phenomena thrown in.
There have been incidents of people stepping through time and stepping back again. Local wormholes, bla bla, it was aliens, yadda yadda. However you explain it, these people have these experiences with echoes of history.
Now I was thinking of a temporal corridor in an urban sprawl that used to be some blue-blood estate, once upon a time. All that remains of the sprawling estates is a neglected "nature strip" in which nature has taken over and turned it into an overgrown mess. Nobody goes there... except my main character.
She's from a solarpunk future, and crawls through a hole in an old stone wall and into the estate-that-was in Eighteen-something-or-other. The wall is part of a decorative feature called a folly. Completely useless structures that were fashionable garden ornaments at the time. Rather like those Buddha heads so that hipsters can pretend they're spiritual, now. [If they were actually spiritual, they'd get the whole Buddha and not just the head]
Anyway, she meets some kids her own age while she's there and does the eternal gamut of kid stuff with them. Neither side asks about the other's attire and they both go home the way they came.
Where the parentals and minders are pretty much "That's nice, sweetie," and carry on.
The visits extend, of course. Future child discovers that the 'park' on the other side of the wall has a manor, has some fun there. The kids of the Victorian era visit "Fairyland" and take advantage of some advanced technology. The Victorian kids take Future Kid to a sideshow, hoping to impress.... and it leads to an arts and crafts session in which they all make some Things In Jars.
Which is about where I reckon some adult should discover what the kids have been up to. Future Kid runs home as the Nanny has the vapours.
Now the story flicks to the adults finally realising that maybe their kids have more than a strange imaginary friend. Future Kid sees a portrait of her friends in an art museum. One of the Victorians shows Mater a "portable shadow show" on a device mistakenly left in the past.
Adults try the corridor that works for the kids. Some kind of profit in mind, of course. Only to discover that the passage doesn't work for them. If you try to go with the intent of messing with time, then you simply can't. Future adult with hippie leanings can go through and just take photos everywhere.
Figuring out how (or if) it's going to end is a problem for later. I might not be writing this until 2030-ish. Depends on how fun the research is.