Butron Castle in Gatica, Biscay Spain. Dating back to the 14th century. It fell into disuse and was later renovated and opened to the public. This proved to be unsuccessful and the building was closed to visitors although the grounds remained open.
Swarovski Kristallwelten - Wattens, Austria. This hides the entrance to the Swarovski Crystals HQ - an amazing experience to visit.