Talavera Maldonado began building an ornate mansion in Salamanca, Spain, in 1493, but didn't live to see it completed, which wasn't until 1517. Its facade is covered with 300 scallop shells, the symbol of the Order of Santiago.
An enduring legend of Casa de las Conchas is that there is a gold coin (or an ounce of gold, according to some sources) hidden underneath each shell. Another widespread legend is that the family that owned the building hid their jewels under one of these shells that adorn the façade, documenting the amount hidden but not the shell where it was located, and whoever wants to find the treasure must provide the amount stipulated as a guarantee in advance. If they find the treasure, they can take it and get their contribution back, otherwise they lose the money left in pledge.
The shells are the most unique feature of Casa de las Conchas, but it also sports intricate grillwork and filigree, coats of arms, and gargoyles. Read about the mansion and see plenty of pictures at Amusing Planet.
(Image credit: Flickr user Jose Luis Cernadas Iglesias)