Falling into the Distance. Mansion of Ghosts and Gold, #1

"It is distance perception, " wrote Uncle Proctor. "Why call it depth unless one can fall there?"The unexplained demise of creepy old Uncle Proctor left a curious inheritance for Orlando and Abigail. All they got was the contents of his library, which included his journal wherein he'd recorded his experiments into the perceptions and trickery of the human mind. Did he really have piles of gold? Lando and Abby were in dire need of at least one gold coin.
So, Lando sets out to recreate those experiments, risking himself and their children and the family dog too. When Lando's tampering with reality uncovers a hidden world, they find old man Proctor trapped there with a bag of gold coins. Proctor insists that Lando save himself and his children, not him, and bring the gold back to his cherished niece, Abigail, who had once danced in his grand foyer as a child, thinking no one was watching.