Palau del Lloctinent, the archives of the Crown of Aragon
The Lloctinent, or Lieutenant, later called the Viceroy, was the representative of the Kings of Spain in Catalunya. He had his own Palau, palace, just next door to the Royal Castle in Barcelona.
Want to know more? Here is what Wiki has to say. It is in Catalan, please use your usual translation devices if you don’t read Catalan.
And this is the Royal Palace, with King Martin’s watchtower.