Forbidden Worlds #50 (1957)

Jo and Nat spend their summer vacation at Nat’s inherited family home on Cullen’s Peak in Maine, a remote, decaying mansion shunned by locals due to its eerie reputation. As strange occurrences unfold—including Nat sleepwalking to the same spot on a road being built across the property and speaking in an old-fashioned sea captain’s voice—Doris begins to worry that something uncanny is stirring beneath the surface.

In a remote corner of Nebraska, a mysterious, impossibly heavy sphere crashes into a haystack, sparking curiosity in local boy Harry Lazarus and his father. When a geologist, Professor Johnson, examines the object under a nuclear microscope, he discovers a hidden world within—complete with rivers, roads, and a ruined city—revealing it to be a tiny, sentient planet that may have been trying to repair itself after impact.