Shadow and others search the rooms thoroughly, but don't find a single item of note.

Well that’s thoroughly frustrating, no secret exits or hidden items :/

lets go go back and try another exit

On the way back, Tyris searches the hallway for any sign of hidden exits. "Nothing says any hidden exit has to be back there," he says with a nod back at the room.

Investigation: 13

Tyris notices something about the eastern wall, but he's not sure. Roll again with an extra +2

Noticing something odd about the eastern wall, Tyris takes a closer look.  21

Tyris finds another hidden doorway opening it he sees...

Four soot-blackened hearths are set into the corners of the room. In front of each rests an anvil and bellows, and implements of the smithing trade hang from nearby hooks. Two barrels of scummy water, once used to cool searing hot iron weapons and implements, stand against the north wall. Two more flank the south exit, and a pair of empty weapon racks stands in the middle of the room.

This maze of a place is frustrating for sure!  Let’s search around the room then the walls

5

15

Tyris checks the barrels to see if anything is in them.

Tyris give me a Investigation check and describe how you check them out. 

Oreus is interested as well and he wants to be sure this tools have been used only for weapons and not for other things (the first thing that pops in his mind are the fake coins somebody saw in the streets): he searches for plates, mold or any other tool that may produce coins.

ooc: I know this is clearly a weapon smith, nevertheless I wrote it for the sake of roleplay

Then he takes a look at the empty racks to understand more or less how many weapons could be produced per time (ooc: roughly: a couple? a gang? an army?)

Finally he goes to the south door to see if there is any rune on it.

Investigation: 11

Tyris walks over to the barrels and starts by simply peering into them to see if anything is visible. If the water is scummy enough he can't see through it, he draws a shortsword and sticks the blade into the water and moves it around to see if it hits anything.

Shadow looks around the room, but doesn't see anything interesting. He then searches for hidden doors again coming up blank, but through the doorway on the southern wall he can see a hallway going east to west and the entrance to a another room 40 feet south of the doorway.

Oreus determines that this forge is mostly for creating weapons and armor, but there are molds for other items as well. However he doesn't find any molds for coins. 

Tyris makes a halfhearted attempt to search the barrels and comes up empty. 

Unable to find anything with his search, tyris looks to the others and says, “watch yourselves.”  Then he tips the barrels over one at a time and dumps them out, aiming them away from himself and the others. 

Everyone can make a perception check (Tyris with advantage)

18 perception

Tyris starts dumping the two barrels of water out onto the floor. The water smells funny. Look at the mess he made he sees only a slipping hazard. Next he dumps the barrel to the west of the doorway. This barrel is not full of water, but ashes. As he dumps it Shadows sees a flash of silver and picks out a small rod engraved with a glyph. Showing it to Oreos, Shadow learns that it is the key to the "I" doors. Tyris dumps the fourth barrel, which just makes the room one big mess.

(No one else needs to roll perception anymore)

Perception: 13

Oreus (trying not to falter) goes to the south door to see if there is any rune on it.

Shadow follows to inspect the door

There is no door, just a doorway leading to a hallway going east to west and another room 40 feet away to the south.