This Lesser-known U.S. Destination Is Hiding the 'Shortest, Deepest River in the World' — and an Underground Cave That Leads to a 'Blue Hole'

"The Lost River Cave offers a unique natural underground boat tour in Kentucky. Visitors can explore the cave and the blue hole, a 437-foot deep natural phenomenon that gives the river its title as the 'shortest, deepest river in the world.' The cave has historical significance, having served various roles throughout history, and sits below a 72-acre park with hiking trails, a butterfly habitat, a playground, and gem mining activities." - Travel + Leisure Editors