The Spell Library of the royal family was hidden in the depths of the Palace.
Being at the heart of the Imperial City, it was natural that the Palace would be heavily guarded. The Elemental Swordsmen outside were merely the external security. In reality, the moment Merlin stepped into the Palace, he had a feeling that he was in the midst of intense potential danger.
There were sure to be many powerful Spell Casters within the Palace who monitored the every movement of anyone who entered the Palace. The fact that Merlin could feel the danger meant his Mind Power was considered decent. Particularly its acuity was much better than most Spell Casters of the same level.
The eighth prince wore a calm and unperturbed expression and was clearly very familiar with the Palace. The many guards that they had encountered bowed respectfully toward the eighth prince.