What do you think of this suggestion for making sense of the Secret Tunnels in the Emerald Grove along with their statues and oil spills:
The secret tunnels were there when the grove was founded. The area where you find the key is a sanctuary; a place of power to Silvanus. Druids would go there to connect with him more, and it is a place of healing; a quiet little spot. The rest of the secret tunnels was a nexus for druids, in the beginning. They could maneuver from the heart of the grove to the forest outside to the caverns and the waterfall entrance relatively easily and quickly through those tunnels. And so, it made the lives of the druids back then easier.
Then the conflict with the Dark Justiciars happened, and the druid leaders realized just how much of a risk the tunnels were. If an enemy came in through there, they could easily overrun every area of the grove in moments.
So the leaders first created the secret doors and hid them behind growth and vines. The doors were then imbued with magic runes. Only those who knew the Animal Friendship spell could pass. Thus, you would have to be a friend of nature to be able to enter the secret passages at all. The stones would not roll away unless someone knew the Animal Friendship spell. This would limit the tunnels to only druids and rangers and such.
But, shadow druids could still get in. So could evil rangers and such. So, the leaders crafted the animal guardian statues, and they placed them along every path within the tunnels. They imbued these statues with the Moonbeam spell which would shoot moonbeams out of the eyes of the statue, blasting enemies with the radiant light that would set them on fire with ghostly flames. (Moonbeam makes way more sense for druids than fire bolts.) Shapechangers, like shadow druids, would be even weaker to these, for they would get disadvantage on resisting the radiant damage. They would also be instantly changed back to original form the first time they were hit.
In order to allow allies through, the druids then made it so regular animals were fine, and so that anyone wearing a Circlet of Nature could pass. These circlets were special to the Emerald Grove. So, any druid of the grove could walk freely in the tunnels without the statues harming them. Any non-animals without a circlet would activate the traps, and so the tunnels became a place where only select druids of the grove were allowed to go; only those granted circlets like Nettie and Findel.
But, then the druid leaders reasoned that if a large enough army found the secret entrance, the statues wouldn't be enough. Therefore, in the dark passages they purposely spilled oil along the main paths, so that if enemies in large numbers came down there, they could be set on fire more easily.
So, what does all this mean mechanically?
1. Statues shoot moonbeams instead of fire bolts.
2. Statues can't be destroyed by arrows or even hacked up with swords.
3. You can't even get into the secret tunnels unless you have a Circlet of Nature or are able to cast Animal Friendship, making the area more of a reward for nature lovers or thieves/murderers who get their hands on one of the circlets.
4. Statues don't harm characters and any allies/enemies within 200 feet of the one wearing the Circlet of Nature.
5. Animals and familiars can move past the statues without getting harmed at all. Ever. This makes familiars and animal companions even more valuable as scouts and such.
6. Statues can be disarmed via the Dispell Magic spell. That's what the spell is for, after all, to dispel traps like this. It still works with the defenses because only IF you have a spellcaster with Dispel Magic and only IF you have a spellcaster with you with Animal Friendship, and only IF you weren't caught off guard by the statues, would you be able to use Dispel Magic on a statue. And then, even then, you might only be able to use Dispel Magic on like one or two of them; certainly not on all.
7. You can't just sneak past the statues. That's dumb. What good are these guardian statues if you can sneak past them? What invading enemy is going to NOT be sneaking when they are entering their enemy's domain?
8. Statues don't set off oil spills and blow you to kingdom come.
9. The key to the chest isn't on some dead guy across that jump down in that alcove. The key is either on Findel or in some hidden nook where the druids hid it.
10. That alcove is a sanctuary to Silvanus which maybe gives some bonuses to Nature, Healing spells, etc. for the remainder of the day. Can be used once a day, thus making the secret tunnels a rewarding area to unlock.
11. The Storage Area in the tunnels is clearly only a temporary storage area, and not meant to be a permanent one, like it seems to be currently. The chest can't even be moved with the staff inside right now. It's like bolted to the floor. So maybe Findel can explain that the "storage area" is only there because the druids are trying to hide some of the best of their things from the tieflings in a place the tieflings can't even go. They're doing this because the tieflings are taking all their stuff; especially the little kids who have formed their own criminal thieving ring.
12. Throw in a bit of backstory with some sort of documents you can find about the secret tunnels describing the things I did above, and we're golden here. The secret tunnels would make more sense, provide players with a challenge and several options to get into them and through them, the traps would use druid magic, they wouldn't be able to be destroyed BY ARROWS, and players would get a good reward if they can figure out how to maneuver through there without dying (meaning they could get the Silvanus sanctuary buff for their party.)