For me
Heavy rain suddenly poured down as soon as midnight struck. Lightning flashing, thunder that continuously boomed and violent winds came as though the god of storm himself was visiting the castle, just without warning. It all came so suddenly that even a passerby would know that this violent thunderstorm was no normal occurrence of nature. It was clear that there was something more to it. Something supernatural.
The now empty castle looked extremely eerie as it stood there in the midst of a violent storm. Wisps of something dark also could be seen lingering all over the structure, very similar to snakes slithering around, in search of something.
In the dungeon, the atmosphere had already become suffocating. The air itself was pulsing with dark energy. It was normally dry and cool down in the dungeon, but now, everyone could feel that it was dense and laced with a smoky quality that irritated their noses.