When I DM I like a two part solve for some of these situations.
1. Low DC perception check. You are in a library, perception check. You don't notice anything about the book cases, but a pile of books next to the desk looks like it hasnt been moved in years. You push the stack, it doesn't move.
2. Investigation check - higher DC, takes longer as well (usually assumed 15 minutes for an investigation check, important when in dungeons or areas with roaming / patrolling creatures). Rotating it all the way to the left and all the way to the right should disengage the bars holding the book case in. If you fail the check:
- It appears to be able to rotate. Do you want to rotate it left or right?
and then they work through it with a chance of success by luck or they can also release the cloud of daggers, 5th level, that is built into it as a magic trap.
