Yep, Eric advice is to wait for the nightfall 

OCC: if Eric is able to prepare his spell, he will cast Clairvoyance to take a look around 

Kriv tries to brush as much of the centipede chunks and goop into the corner of the room. He takes a seat and conjures some words that hang in the air for a minute before disappearing. The message reads, What is our plan? Just follow the lizards and fight?

"Since we decided to wait so as not to risk arousing suspicion, I think we will have to rely completely on Snapjaw's greater knowledge of the location afterwards" Khessa replies, in a low voice. "Objectively, he has been here longer than us and has a clearer idea of the situation ... His plan might be simplistic, but should be free from gross errors".

"Also, Eric claims he can take a look around with magic..." the blonde arcane warrior approaches her beloved "Let's see if he discovers anything interesting".

Calvin took the opportunity to share all that remembers regarding Tiamut.

"Sometimes the most simple plans are the ones that work," Calvin replies to Khessa. "The more complex a plan the more opportunity things can go awry. 

So you wait for nightfall. At various times during this period you will hear (different) drumbeats that can be heard throughout the castle. You don't know what they mean, but you do recall that Snapjaw asked you to meet him "at the Arsenal in the northeasterly tower".

I think Eric intended to use Clairvoyance to take a look around, as he had planned to do a few posts ago. Is he able to see anything interesting?

OCC: Tecnically Eric still need to prepare the Clairvoyance spell. if he is able to do it in the time the other rest and clean up he'll do it, otherwise he just suggest to join the Snapjaw at the Arsenal. Also I forgot about the meeting point, I thought it was in our room... in this case Eric would have suggest to rest and leave the room slightly before the nightfall to meet our Lizardfolk friend.

Zale nods in agreement with Calvin and Khessa's comments, then says, "Eye, let's hold here until that meeting with Snapjaw."

Clairvoyance also doesn't move around, so he place a sensor in one of the rooms in castle that Eric already knows. Or an obvious room he doesn't know (like a room behind a door you've seen).

Here's a map for reference:

OCC: I though you could move the sensor around... I have misinterpreted, my fault  :P

Never mind then...

In this case... Snapjaw told us where the 'Arsenal' is? Because if he didn't and if we can't see it with Clairvoyance, we'd better ask someone directions while it's daytime... Asking at night would be much more suspicious - as would be opening doors at random.

"He mentioned the north-east tower" says the dwarf. Once the nightfall approaches he says "time to go, just head to the north-east tower with nonchalance, I'm positive we'll meet our Lizard friend there" 

OCC: remember that the party is affected by Eric's motivational speech for one hour after leaving the room

Feeling more motivated than ever, Khessa follows her beloved dwarf, staying by his side.

Kriv gathers the centipede parts into his arms. At first he tries to avoid the guts and goopy parts, but gives up quickly. “Just going through the castle to make sure we rid it of bugs and other annoyances.”

Calvin shrugs his shoulders, the northeast tower would be the best plan. He then follows the group through the castle to the northeast tower.

[[ Small correction from my part. It seems that the maps are on their side (North is to the right). The NE tower is your correct destination, but it's in the bottom right ]]

Verry well. When the sun sets you go back to the Hall where Cultists are in process of leaving the room. A guard comes from the Inner Ward with 2 Guard Drakes. He explains that they'll guard the Hall the will attack everyting that moves unless he's with you. You thank him for the information and move to the Outer Ward. From there you take the door that seems to lead to the tower. The room seems to be a forgde and armory. A large forge dominates the center of this chamber, which is pleasantly warm thanks to a bed of coals glowing dully in the forge. Half a dozen Lizardfolk are working around the forge, but they don’t seem to be accomplishing much. Other accouterments of the blacksmith’s trade are scattered through the room, and many very poorly made metal items are heaped in the northwest corner.  

The dwarf seems relieved to see the forge and approaches, welcoming the heat of the living fire "well, you seems to have quite good starting point here! It seems that what you need is just a seasoned blacksmith! maybe I could help... feel free to ask!"  he says loud to the Lizardfolks 

Khessa, under the pretense of thanking the guard with 2 Guard Drakes, looks at him carefully to remember what he looks like.

Once they reach the meeting place, she shares with the companions: "The 2 Guard Drakes who guard the Hall... If we meet them alone, I can take on the appearance of their master... perhaps this way we can pass without them attacking us".

The Lizardfolk don't speak Common but they get that you're trying to help them. They show their work: it looks like they  are trying to make an iron spear point from scraps of ruined armor, but their effort is producing something more like a shovel than a blade.

Patiently, but without hiding his excitement for attending an actual forge after quite a long time, Eric starts working at the forge, showing them how to realize their blades properly.

He uses his Artisan Blessing to create a proper spear of the finest quality possible 

"You see, my friends" says by showing it to them : " fire is the greatest gift of the Gods, through it and thanks to it you can bend the strongest of the mineral at will, creating tools for peace and weapons for battle! With time and practice, a skilled blacksmith is able to catch the sparkles of the divine fire, a fragment of the eternity!" he says with enthusiasm.