I can see the point of going abroad if you want to lounge around on a beach and swim in hot weather; the UK is not great for that.
But for everything else, we do the same kind of things on foreign holidays as we do on ones in the UK. Museums, historic sites, walking and so on.
You get out what you put in. Manchester is setting up a new football museum and we will not be going because I don't know anything about football, don't have any interest in it and so the museum would have to do something really impressive for my family to get anything out of it.
I suspect it is the same for other museums, NT properties, areas of the countryside and so on. If you are bringing something to it, something you and your kids are interested in and want to know more about, then you go and find it. But if you turn up with no particular interest, then it is unlikely your interest is going to be much sparked just because they have put together a colouring in table, an overpriced cafe and a couple of information signs with some tactile kids' display.
I found it easier when the kids were younger and we were engaging it with it at a more basic level - teaching them how to read maps or basics of history. I'm trying to work out how to approach it all from a different angle with secondary school children with diverging interests. As DS has moved more into art, I'm thinking of going around stuff with sketch books and getting them to pick themes - birds, clothing, the supernatural or whatever, and getting them to sketch from one theme at different locations - outdoors, museums, different historic sites and so on. But you have to bring something to it, even at theme parks we love the theming and how people go about imagining it all and developing it around roller coasters.