I’m reviving all my favorite series! That’s right, Myth or Magic is back again!
“The princess and the people in the castle fall into a sleep for 100 years, but what happens to all the food in the castle, or the furniture, or the castle walls? Wouldn’t it all decay and rot away? What kind of condition would the castle be in after 100 years being exposed to the elements with no upkeep or repairs?” -Kat

Great question, Kat, thanks for asking! If any of you have your own fairy tale questions, leave them in the comments!
I’ll start with what I know for sure.
The food did not rot away.
In both the Grimm version and the Perrault version, the good fairy who prevented Sleeping Beauty’s death caused all the castle to fall into slumber with her. Both versions specifically state that she caused the fires and the foods cooking them also fell . . . well, asleep, for lack of a better term.
As for the castle itself, well, this is really more just speculation. The Grimm version of the tale says that even the wind and plants went dormant, which makes me think weather and other forces of nature wouldn’t affect the castle.
Since the fairy is going to such lengths to preserve the things and people around the sleeping princess, it makes sense that it would include the castle as well.
So, to reduce it down to a single word: magic.
I know, it’s kind of a cop out, but to me, it’s what makes the most sense.