Lily's perspective.
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It didn't take that long for Lily to find the secret door. It was only five minutes of sneaking around. The servants were much too casual, and the clues for the hidden door easily found by someone that had eyes at ankle height. In one of the hallways, there was a display case between two rooms. It showed off a number of poorly done clay sculptures and water colour paintings. If Lily was all but certain the display case was for little arts and crafts projects Bing and Feng made growing up.
It was actually rather sweet. The secret to the vault wasn't behind the suits of armour, the legendary blades, or the medicinal pills cabinet. It was behind the deeply personal examples of Bing and Feng's childhood. Lily felt her respect for Meng and Bang, the real ones, rise by a good margin at the discovery.