before everyone leaves for the gala...
From your desk chair:
Four steps towards the window. Pivot right. Walk to the shelves. Crouch down to the second shelf from the ground. Move the scrolls left and the books right. Lift the calligraphy scroll from the wall without removing it completely from the wall. You will see a faint shimmer. There will be handle beneath an embedded genjutsu. Pull the handle towards you until it clicks. Turn counterclockwise 120° until it clicks twice. Pull the handle slowly towards you as the bottom shelves will swing out.
Given the dust inside, you may correctly surmise this particular cache's existence is not widely known.
[also inside the hidey-hole:]
[my my my, how did that get there...?]