Jerigg moves his hand and an ethereal one appears in the air, then he opens the door with it. Just to reveal a solid wall behind it. 

I search the solid wall 10

Falmo will ask Jerigg to tap the wall with mage hand, watching closely to see what happens: 20 or 17

(Falmo sees through the wall, somehow.)

I smack he wall with full force using my crowbar =)

Bored, Ubogri heads back to the crossroads and then east, keeping an eye for any trouble or anything of interest.

Perception: 18

You both check the wall behind the door and after hitting it with the crowbar Falmo notices that it moved a bit. You both push the wall and it slides revealing a long corridor that keeps going north. 

Ubogri, in the meantime, decided to go back and then east. After 40/50 feet he arrives at a door, he opens it and continues down the corridor for pretty much the same distance as before just to turn right and arrive in what looks to be an underground grotto. A thick silver mist, shot through with delicate streamers of gold, partially blocks your view of the area that lies ahead, so you can't see very well what's inside. 

Another blasted mist. Ubogri goes back to the crossroads and then south.

South the corridor ends with yet another door.

Ubogri heads north to find the others.

"The thick mist here could be hazardous." Lumiere says. She holds her hand up. "Should we attempt to see if the mist reacts to anything from a distance?"

Falmo will toss a single arrow into the mist.

I join the group at the mist and forcefully throw in a javelin with light cast on it.

Does it clatter to the floor down the hall? Does it hit anything? Do we lose sight of it?

OOC: Wait, you three aren't at the mist. Ubogri went down another passage and found the mist. You three were at the wall that slid away after opening the door.

OOC: Yeah, then everybody decided to follow you, so I followed them.

The mists makes the entire area heavily obscured, but you can follow both the arrow and the javelin for a bit before they disappear out of sight just to fall on the ground with an echoing sound moments later. 

"Yeah, forget that." I go back to the loose door and check it out with detect magic

The door doesn't appear to be magical 

"It looks like we should attempt to enter again." Lumiere advises using the Mage Hand to push the door open once again.

(Not sure why you think it's closed!)

South there's a closed door, east there's the mist cavern, north there's the door that hid a wall with a secret passage in it

Go through the non-magical door.