Castiel doesn't hear any movement, or any soft footsteps for how stealthy the occupant of the castle is, so it's all soft, thick silence and dimness that's difficult to see through, especially as his vision is adjusting from the light of the outdoors. He squints into the shadows when he thinks he sees movement, a flutter in the darkness, but no sound comes, and no one moves to greet him.

Glancing back toward the door, he presses a palm to Aaron's warm muzzle before he's venturing further inside, one hand clutching his cloak more tightly closed, his footsteps echoing against the tall stone walls, ringing into the vaulted ceilings above.

"Hello?" he calls into the darkness, his head turning quickly when he sees what he thinks is a flash of green in the dark, but he can't be sure. The castle seems for all intents and purposes empty, for the lack of life and sound, but something still feels alive, his natural intuition hinting to him, twitching nervously, and Castiel swallows dryly as he steps further into the foyer. "Is anyone here?"