Background: The players were told what three keys they need for the vault, one of which is a drow's finger. They spent a day researching where they could possibly find a drow finger. I said they heard two rumors: 1) The Xanathar's Lair had hired a drow adviser and 2) There were sightings of drow in the Dock Ward. They chose to head straight into the sewers. They then used the Stone of Golorr to ask about the Xanathar's Lair and learned it's somewhere under the Castle Ward.

Now, they're wandering the sewers toward/underneath the Castle Ward. They don't have a guide and don't know about the secret entrance into the Xanathar's Lair (or any entrance into Xanathar's Lair).

My initial thought is to have them wander perpetually because they have no way to know about the secret entrance. Is that the best way to handle this? Should I retcon what the Stone of Golorr told them so they know where the secret entrance is? What do you think?