“Coral Castle”:http://www.crystalinks.com/coralcastle.html would be my guess at the answer for the Blogathon’s Game 11, which is a Google puzzle in which the clue is:

bq. In Florida, at night, unseen
He built it for his “sweet sixteen”
He levered tons of coral stone
And there he lived and died alone

If you follow the link it has pictures of the _Coral Castle_ and it says:

bq. _Coral Castle was built in the early 20th century by an eccentric Latvian recluse named Edward Leedskalnin who allegedly left Latvia when he was rejected by his 16 year old fiance. He would never marry and would spend 30 years of his life building a Coral Castle and its surrounding buildings, for his alleged ‘Sweet Sixteen’. Leaving for America, he came down with terminal tuberculosis. He allegedly spontaneously healed, stating that magnets had some effect on his healing._