Coral Castle
The 8-ton gate is carved so precisely that it fits within a quarter of an inch of the walls on both sides. It was so well-balanced that a child could open it with the push of a single finger. The mystery of the gate's perfectly balanced axis and the amazing ease with which it revolved lasted for decades until the gate suddenly stopped working in 1986. At that time, a team of engineers was brought in for consultation. In order to remove the gate, six men and a 50-short-ton (45 t) crane were utilized. Once the gate was removed, the engineers discovered how Leedskalnin had centered and balanced the 9-short-ton piece of rock. Leedskalnin had drilled a hole from top to bottom of the 8-foot-tall gate with no electric tools and inserted a metal shaft. The rock rested on an old truck bearing. It was the rusting out of this bearing that resulted in the gate's failure to revolve. The 9-short-ton gate, complete with new bearings, and a replaced shaft was lifted and set back into place on July 23, 1986.[13] The gate failed again in 2005 and was subsequently repaired, however it does not rotate with the same ease it once did.