Thousands of caves can be found throughout the United States. Each one is a unique subterranean environment that may include enormous chambers, tight tunnels, underground rivers and waterfalls, unique animals, or other natural wonders. It's no surprise that humans throughout history have explored caves. The recreational sport of exploring caves is known as caving or spelunking. Anyone can enjoy caving, which offers adventurous experiences for all levels. In the United States, more than one hundred caves are open to the public. People can explore them by participating in guided tours or by following marked paths. This is a great way to get started with caving and to experience the sport firsthand. Those seeking more adventure can join caving clubs to learn advanced caving skills and connect to others who share their passion. The National Speleological Society sponsors over two hundred caving clubs in the United States. These clubs organize excursions to caves that are not open to the public, and advanced spelunkers may even get the chance to explore parts of caves that have never been seen before. Caving clubs also promote conservation; as a general rule, people should never leave anything behind in caves, never take anything out, and never damage any rock formations. Caving requires special equipment. For example, it is very important to have a source of light when exploring a dark cave. Cavers need to wear a well-fitted helmet with a headlamp. Back-ups for light sources, which can include extra batteries, flashlights, and glow sticks, are also important. Caves often get cold and can be very wet, so rugged, waterproof clothing, including sturdy hiking boots, is recommended. Other items to bring include enough food and water for the excursion, a small first aid kit, and a map of the cave. Caving can be a very safe sport when participants are well informed, cautious, and prepared. No one should explore a cave alone; it is best to explore in small groups of four to six people, and every expedition should have a