D&D 5E Chapter Three of Lost Mines of Phandelver is Frustrating

[Nemio]

But if you do what my group did (kidnap a goblin from Chapter 1 and interrogate him, given that the adventure book even says that they can give you rough directions to Cragmaw Castle) that problem is already solved, so if your heroes aren't necessarily that heroic

Those rough directions were played out in the official WOTC playthrough.
A captured goblin said he knew the castle was "somewhere between where the sun never shines and where it comes up"

That's very vague and the risk of getting lost (and getting random encounters) is high which the DM told them.
That group didn't take the risk and neither did mine.

It's too late now but just letting you know.

 

[Charles Rampant]

To be honest, this thread confuses me. Chapter three is the best part of Lost Mines! The players suddenly get the freedom to decide their own direction and path, in the light of quests given by people that they have a range of opinions towards. They have to collectively decide what to do, in what order, and whether they can afford to do so with Gundren still in the wind. It represents the core of a good adventure, that is the player agency coupled with a fun story. If you remove chapter three, then the adventure is the worse for it, since now you've got a story with no way for the players to step off the tracks for a moment. They do A, B, C, and D in that order; chapter 3 offers E, F, G, and H, to be inserted in whichever order the players want.

 

[CydKnight]

If the side quests are really that big of a thorn in the momentum of your adventure, you may simply have to skip some of them. Having run Lost Mine of Phandelver myself, I completely agree that they are not all necessary to complete the adventure. To offset the lack of leveling up by skipping any side quests, you could have your characters start at a higher level alleviating the need to level up within the adventure.

 

[Jer]

Actually, I'd probably let the players just do what they want - if they know where Cragmaw is and want to go right to it, more power to them.

But I would do two other things. First I would also take a look at the threat level of the encounters in the castle and compare it to where they are. And if they're substantially below the power level I think would be needed to hit the castle, I'd try to find a way to telegraph that to them. In game by making sure that the first encounter is actually representative of the rest of the encounters they'll be seeing (i.e. if it's an easy one comparatively, make it tougher), or out of game by saying "guys, just FYI - the castle is pretty difficult and assumes you'll have leveled up on some of these side quests" (it really depends on the dynamic of your group and what they prefer at the table). If after being telegraphed that it's really damn hard they keep pushing anyway, well, that's D&D - TPKs are part of the game - but chances are a tough first encounter will have them scurrying back to build up their power level a bit before coming back.

Which leads into the second thing I would do, which is take a look at the player and character motivations for your group and try to fold, spindle and mutilate the side-quests into things that either the player would want to do or that the character would want to do. If they're not the "heroic" type then maybe they're the "mercenary" type - have someone pay them to go do one of the side quests. Or if they're the greedy type, spread some rumors of magic items around and see if they bite (I might even throw an extra magic item into the side quest to pay off one of the rumors, because hey why not? It makes it easier to lead the PCs where you want them if they think there's a good chance of a magic item they might want at the end, and if you never pay out they'll stop biting at the bait). This actually works pretty well with the "scare them with a tough encounter" tactic above, because that can lead to "ok, the castle is too tough - but there are rumors of a magic sword/armor/whatever over here, and maybe if we find that we'll be able to tackle the castle" and that again makes it their decision to go off and do it instead of just a plot hammer.

This attacks the "problem" from two places - it has the potential to turn the side quests into character-driven events instead of plot-driven ones, and it lets the players feel like they're making their own decisions with good information in front of them and have a narrative reason for delaying the frontal assault that they could have done right after chapter 1.

 

[Staccat0]

My players did exactly as yours OP and had no issues with Cragmaw. They are total idiots too, so I think any players should be fine.