The different types of features that decorate the cave are collectively called cave formations or speleothems.
Most of the speleothems in the cave form by similar processes. The water passes downward through the soil above the limestone, absorbs carbon dioxide, and becomes acidic. As a weak acid, the water is able to dissolve a small amount of the limestone rock as it passes through cracks and pores on its journey down into the cave. As this water drips into the air-filled cave, dissolved carbon dioxide is given off. Because the water has lost carbon dioxide, it cannot hold as much dissolved calcium. The excess calcium is them precipitated on the cave walls and ceilings to make up many of the different kinds of formations. Most calcium is precipitated in the cave as the mineral calcite (CaCO3).
The speloeothem that Wind Cave is most famous for is boxwork. There are many other formations such as popcorn, frostwork, dogtooth spar crystals, and flowstone that may be seen along the tour routes. Other speleothems that can be seen in the cave, but not on the tour route, are: helictite bushes, calcite rafts, and gypsum features. Below are pictures of some of the more common decorations (speleothems) of Wind Cave. Clicking on the picture will take you to link with more explanations about the formation.