Limestone formation of small stalactites hanging down from a spine in Luray Caverns in Shenandoah Valley, Virginia.

The hollowing-out of a limestone cave begins as this acidified water percolates through the limestone, dissolving and eroding layers along the way. The water fills every opening, enlarging the existing crevices, and descends into lower levels of the earth leaving huge limestone chambers. As the water subsides, and only slow seepage continues, nature's decorating process begins. Luray Caverns were discovered on August 13, 1878.

References: Cavern Creation on Luray Caverns - Luray Caverns on Britannica