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Today for Father's Day, I took my Dad to Moaning Cavern, in Calaveras County, California. This was a spacious vertical shaft 165 feet tall, which is descended by a combination of stairs and a unique 100-foot-high (30 m) spiral staircase built in the early 1900s. It was a tight fit, in some cases, while descending, and quite a challenge to climb back up, but it was still an amazingly beautiful cavern.