Cutting the vines that secured the creature you see that it is a grung.  He immediately grovels at your feet and speaks in a language none of you understand.

"Dankie dankie sterkste. Ek is ewig in yopur skuld. My vader is 'n groot koning en hy sal jou met geskenke en goud stort om my lewe te red."

He gestures to the north.

"Ahbut young Jacques Cousteau stand up and let me check you out before we head north" Dr A says to the young grung. 

"It sounds like he's thanking us. I think we've found the grung king's son!"

The grung cocks his head as if he doesn't understand what you are saying.  He continues to gesture to the north.

Timber walks up to the grung, and to the best of his ability uses Minor Illusion to create an item that would have represented the grung king's royalty and shows it to the grung, in hopes he might recognise the object.

The grung nods his head at the image and jumps up and down excitedly as he continues gesturing to the north in the direction of the king's shrine.

Dr A watches the young Grung bounce up and down like an Energiser Bunny "ahbut the enthusiasm of the young never ceases to bring a smile to these tired old eyes!" 

Kirinar leads the group back to the grung stronghold, watching for any more dangers.

Timber grins when then grung recognises his image and turns to the group, "I think he wants us to go north. Maybe that is where the next cube is?"

"It is nearly dark now."  says Artus.  "It is likely far more unsafe to travel at night than during the day.  Do we seek a safe place to sleep or risk trying to get back to the shrine?"

"Guess it depends on the young one here. If Mr. Froggy wants to go home now, then I feel its only right to go with him and watch out for him. If we can get him to stay with us fort he night, then we can hole up someplace safe. But who's gonna tell him that?"

"Ahbut fgiven young Jacques Cousteau's level of excitement I don't think he'll hang around until morning?" Dr A responds.

"Let  me have a go" Dr A says to Kirinar tapping the Helm of Telepathy.

"Ahbut young Jacques, it is not safe to travel at night. We will wait here until the morning and then take you father tomorrow!" Dr A thinks - via the Helm of Telepathy - at the young Grung.

16

The grung looks at the large Tortle standing before it and suddenly he nods, seeming to understand what you have said to him.  You don't get the impression that you can exactly communicate with each other, but he does seem to understand what you are trying to communicate.

You are able to find an empty building to spend the night.  Setting up watches you safely make it till morning.  After breaking your fast you head towards the shrine that you hope still holds the final cube you need to enter the secret tombs underneath Omu.  

About halfway back to the shrine you encounter several grung that appear to be a hunting party.  But they quickly recognize the young grung with you and escort you back to the shrine that is their home.

Chief Yorb is delighted to have his son back and as promised allows you access to the inner shrine that he has never been inside of.

Moving up the slippery steps you enter the area of the shrine that the grung's live in (18B)

Torches shed light over rooms filled of treasure: chests heaped with coins, polished amphorae, strings of pearls, and ornate pieces of armor. Set into the floor in front of another double door is a mosaic depicting a frog-like humanoid beating a leopard that has snakes emerging from its shoulders. Cuneiform inscriptions are woven above and below the combatants.

The inscriptions are written in Old Omuan. The one above the mosaic reads, “Nangnang teaches us to serve only ourselves.” The inscriptions below tell how Nangnang (a grung) stole a spear belonging to Shagambi (a kamadan). 

The stone doors to area 18C are locked, with neither keyhole nor handle. Above the double door, the following message is carved into the stonework in Old Omuan: “Whoever among you is the richest, bring me your gifts.”

"There's something fishy about this," Keyleth says to no one in particular. "All of this treasure just sitting here... why hasn't it been looted by explorers or any of the inhabitants of this city?"

Looking around at the treasure scattered about, does it appear to be genuine, or fake, or illusory (to the extent that Keyleth can tell)?

Investigation: 28

Also, is the rectangular platform/pedestal in front of the double doors something we can see?

Keyleth can see nothing to indicate that the treasure is not real.  The rectangular platform is just that, a stone table with no inscriptions and Keyleth finds nothing of interest about it.

"Look for a spear," Kirinar says. "Like the picture - maybe the richest prize here is the spear Nangnang stole!"

"Ahbut if I remember correctly this Nangnang is a selfish sort and doesn't like to share. So even if we find the spear we'll probably have to swap it for something." Dr A comments. Looking at the inscription he continues "I'm rich in knowledge but I don't think that is exactly what he is referring to!"