As tempting as it is to view the amazing park through a veil of mystery, in fact we know how the castle was built. Creating a structure like the Coral Castle today could probably be accomplished in a few months with a construction crew and modern machinery. But Leedskalnin worked alone using basic tools like picks, winches, ropes and pulleys.
Leedskalnin himself said that that he did it using hard work and the principles of leverage. The tools he used to quarry the rock are on display at the Coral Castle, and several old photos depict the large tripods, pulleys, and winches he used to move the blocks. Though the quarried stone slabs are large, they are actually lighter than they appear because the rock is porous." Source: Live Science