With seamless flow, the rhymes of this wonder-filled story invite elementary-aged readers to join two young siblings on a guided tour of a subterranean cave and marvel at the ecosystem that lies quietly beneath the surface. Voiced from the perspective of one of the siblings, this story offers readers an impressive way to immerse themselves in the atmosphere and life of the cave, encountering formations and underground creatures. Choice action words detail the characters' journey and reactions, while some words swirl and bend to match the named sights or nature of the depicted element. The digital illustrations change points of view to match the movements of the three main characters, often positioning them to catch wider angles of the cave and its inhabitants in the light of the trio's flashlights. The characters have easy-to-read, frequent expressions of delight or momentary trepidation, while the lights they carry direct readers' attentions to the cave's features and textured elements, realistically surrounded by dark spaces and shadows that ripple with rock forms and a filtered glow. A note at the end explains the importance of cave conservation, while a vocabulary page covers geology terms. VERDICT An inspiring companion story for lessons about diverse ecosystems. With its unique focus on caves and guided exploration, this hybrid book fuels the imagination with its smooth, poetic rhymes that will intrigue any novice geologist.-Rachel Mulligan, School Library Journal