The Santa's Workshop is a limited edition building available in FarmVille. It was originally released as part of the Winter Holiday Event. It's also possible you find one in the 7th generation mystery box that you can get from the Holiday Tree Presents.
It was re-released on the December 11th, 2011 as part of the Winter Holiday Event (2011) available from the market to purchase for 38 cash and 2,000 experience gain, with value 10,000 coins re-sell.