[Mirror, Mirror]
Darsy

There are, in fact, at least two pairs of footsteps. Thanks to the nature of this area's echo, it's hard to exactly know for sure exactly where they are, but they're in that direction. Over time, the footstep sounds get a little louder or more frequent, which could mean any number of things.

The mirror's image is frozen of Darsy standing back a bit. I imagine that's pretty strange. After tapping on it, Darsy will definitely be able to notice something else odd about it. Even though the image of her is frozen, there's still some movement in the background of the reflection. Little shadows cast differently, or the reflection in the water changing, or a little animal running across the way.


Card

Upon exiting this servant's-only room, Card will find himself in a hallway of a similar style, which was obviously used by the servants to enter and exit whichever room on the ground floor or the other floors they want. There's hallways, trapdoors, staircases, narrow ways to come in and out of rooms and behind bookcases, false doorways, and so on.

The largest and most obvious other passageway that he might find will lead to the library. The second largest will lead to the kitchen. The fifth most obvious leads to the dungeon, which is roughly where Darsy is right now. If he needs a reason to go there instead of the other places, it's possible he'll be able to hear the footsteps if he goes close enough to the dungeon area.

Or, in other words, you get to choose out of these three rooms where he goes now.