The Eastern Palace was neither particularly large nor particularly small.
It was considered large because it was, after all, the residence of the future ruler of a nation; if it were not sufficiently grand, it would bring shame to the entire country.
It was deemed small because the place, which should have been occupied solely by the Crown Prince, now housed three Imperial Princes, as well as Feng Chaonan, the Prince in all but name.
These four, along with their respective subordinates, made the vast Eastern Palace seem somewhat crowded.
At such close proximity, with Qing Yu's abilities, moving in and out without a trace was an easy feat.
Just as with her previous stealthy night visit to Feng Chaonan, if Qing Yu wished, no one would know she had been there.
