Take a half-mile walk into the center of Lookout Mountain to the largest underground waterfall in the United States. This 145-foot fall funnels 300 gallons of water per minute into a subterranean river. The gorgeous falls are highlighted with colored lights and a reflecting pool. There is a 10-story observation tower, Ruby Falls Fun Forest for kids, and walking tour through the caverns, which lasts one and one-half hours. Admission charges are: $11.50 for adults; $5.50 for children.