Several books use the concept of a magical door to provide characters entry into other worlds, or to better places in this one. Exit West, a timely novel about refugees by Man Booker Prize winner Mohsin Hamid, employs this device—but because of the power of his plotting and beauty of his prose, it's highly believable.
The novel begins when a young man, Saeed, meets Nadia in an adult evening class in an unnamed country at some point in the near future. Civil war wracks the country; terrorists and militants roam the streets. Read more about Exit West