Floating Castle: A good way to get coins and SDB's.
Lots of folks built these then deleted them once the prompt shows them only receiving Gems which are more or less worthless. They didn't bother reading the small type that said 6 SDB's as well as the Gems.
And no, the Gem Tower is no longer offered in the Market Place but GEM Packs are?
Pity the poor fool that spends farm cash for one of these "Gem Packs". BTW, I sell the 84 Gems I receive each day for 0 coins.