The Phantom Tower (Unabridged‪)‬

Twin brothers discover their new home is also a portal--for an hour a day--to a parallel dimension in this spine-chilling middle-grade adventure, perfect for fans of The Mysterious Benedict Society

Twelve-year-old twins Colm and Mal might look identical, but they’re different in just about every other way. The one thing they can agree on is that neither brother wants to move to Chicago for a fresh start with their mom two years after their dad’s death.
 
The boys soon discover that their new apartment building, Brunhild Tower, is full of strange quirks: a mysterious Princess who warns them not to wander the building at midday, eerie sounds coming from the walls, and an elevator that’s missing a button for the thirteenth floor. Then one afternoon, that button appears, catapulting the brothers and their inquisitive new neighbor, Tamika, into a parallel dimension and a twin building stuck in time, where the spirits of all the former residents of Brunhild Tower live on, trapped by an ancient curse. Now, Colm, Mal, and Tamika must race against time to solve the mystery of the phantom tower—or risk spending an eternity as ghosts themselves.