This add-on to Elusand was a free print-and-play expansion. The expansion was made available on the Catan.com website and contains four extra buildings:

Castle (Burg): Pay 2 gold for 1 influence card or vice versa
Barracks (Kaserne): Take 1 gold or 1 influence card
Warehouse (Lager, 2x): 1 additional trade point

I understand this hard copy set was a give-away at Spiel. It is unknown whether Catan consider this an official giveaway or whether they just made up some sets to show people and at the end let people keep them.