I recognize that this may be a subjective question, but since its dealing with a published book I'm curious if there are things that I missed within the published material itself.
I'm running PotA for my group and they have tackled the Hidden Keeps. After the first one they went down into the depths (assuming it was the way they were supposed to go) and entered a dungeon that was significantly higher than their level 3 characters could tackle. I had to do a big fanfare of premonition for members of the party to realize they were not where they were supposed to be and let them leave the dungeon. Now the players are gun shy.
As a new DM, did I miss something? How was I supposed to gate this? Right now it looks like a design flaw in the writing. Should I expect this in future published works as well?