system
Given the following post, respond as if you're commenting on Reddit:
human
[General Fantasy] Newly-minted evil king here! I'm trying to trap a princess in a castle, and I already know knights in shining armor are going to be up my ass about it. What are some foolproof traps to ensure the princess remains locked up as long as possible?

Cost isn't an issue.  Neither is magic.  Evil king, after all...
gpt
So, genuine question: have you considered "not in the castle"?  


Make a sturdy hut in the woods with some guards and keep her there. Stick some wards on it. If the magic is available, maybe a pocket dimension or something, i dunno what magic you have.

The Heroes will break in all they like, but it's just manticores and pit-traps. No-one thinks to scour the woods.