In my book there's a portal to a fantasy world in a mansion. I was told this was done to death, though I can not find any books with that exact setting?
Even if it is done to death, does that make you not want to use it still? It's called writing what you know. Just write it. Don't listen to what others are saying, unless they are saying it is the mirror image of another story.
The Magician's Nephew and The Lion, the Witch, and the Wardrobe are classic examples. But lots of things have been done more than once. Just make your story unique.
It is how you tell the story that matters. Edgar Allen Poe wrote about the death of a beautiful woman. Again and again.
I think they count. They are two different stories, with two different portals. Within that series...every book (except A Horse and His Boy) has a portal within a mansion. This does not mean that the OP should not write the story.
Yes its been done to death, but mostly everything has in one form or another. If you want to write it then do it, and if its good then it'll be good, unless its a direct rip-off of course. It will be good for you either way, the more you write the more you improve!
It is impossible, these days, to write a completely unique story. Every plotline has been done multiple times before. What matters is refreshing the idea and making it your own and make the reader want to hear it.
Find an idea that hasn't been done to death. There's no such thing as a truly unique idea. It's what you do with the idea itself that makes it unique. Portal in a mansion? Yeah, it's been done. But not all portals lead to the same place. If the rest of your characters and plot events are well developed and well written, then that's what makes up for doing an idea that's been done plenty of times before.
Portals? Mansions? Fantasy Worlds? Why not! It has been done many times yes. But, its still a cool idea and if thats what you want to do, go for it!
Mirror of her Dreams Alice in Wonderland Those are just off the top of my head. I'm sure there are more. Write what you want. In truth, isn't it the fantasy story on the other side of the portal that counts? It's just like in Science Ficiton, having a hyperdrive/hyperspace for travel great distances between planets. It's a plot device.
So why is the portal in a mansion? Are the rich owners of the mansion people who have been secretly exploring the fantasy world and using its technology to make money?
If you're hesitating, think about why you chose it to be in a mansion. If there is a reason to it, if it's a part of the story and you would have to ajdust the plot a lot were you to put it somewhere else, then go ahead, it belongs there. If it could be anywhere else and the story would work just the same, then it's time to consider other options, maybe you'll come up with one that you like even more.
when you said that I straight away thought of the Lion, the Witch, and the Wardrobe ... though I can't remember if that was in a mansion or not. I think everything in fiction, particularly fantasy, has been done to death you just have to put your own personal spin on it to make it original.
I'm absolutely sure that it's been done several times. The Narnia books already mentioned, Through the Looking glass, two or three books that I read as a child and can't remember, and probably a dozen more times that I don't know about. If you ignore the portal in the mansion and just do the hidden world, there are probably at least a dozen more. And none of that matters. Where would mystery writers be if they worried, "I wanted to write about a person being murdered and the police trying to find out who did it, but I hear it's been done."? Everything's been done. Do it anyway.
