Writing about other worlds is common. But getting people into other worlds in interesting - and somewhat novel - ways is becoming harder and harder. C.S. Lewis alone grabbed two of the coolest methods all by himself.
First, he reached another world through a magic portal (i.e. the wardrobe). While I’m not suggesting that he was the first to utilize this device, his Chronicles of Narnia series is surely one of the first things to come to mind when the concept is brought up. Today even the most popular books rely on a similar mechanism. Platform 9 3/4 at King’s Cross is a great example. There’s nothing wrong with that, but there are times when I wish the wardrobe was still available.
Second, and less well known, Lewis reached another place in our own universe which was unknown enough that it could still serve as a place of mystery, other-worldly fantasy, and even a kind of magical land, despite the fact that the locale itself was as real as the ground you are standing on. I am of course referring to the Space Trilogy where the stories take place on Mars, Venus and finally, Earth.
I doubt Lewis would have written Out of The Silent Planet- a tale of life and adventure on Mars - today. At least he may not have set it on Mars. Too much is known today. He wrote at a time when it was still possible that maybe we did not know everything there was to know about Mars or Venus. Because of when he wrote, there was still a bit of mystery surrounding our galactic siblings. Today similar tales rely almost entirely on imagination because the mystery is all but gone. It can still be done, though it is far more difficult, having lost the aid of legitimate mystery. The original War of the Worlds offered a particular kind of dread that modern remakes will never have because there was a time when, maybe, just maybe, something could be lurking on Mars ready to invade.
All that to say, I am having a heck of a time coming up with a relatively unique and novel way for my new characters to get into another world.
That loss of mystery is a loss for fantasy and science fiction.