i'm in the fortress but i can't get inside!

how do i open the gate?

which fortress and which gate?
|
|
|
|
|
|
|
|
S
P
O
I
L
E
R
S
|
|
|
If you mean the aurilite ice fortress and are in the room with the white abishai
i'm given to understand you have to rest there and wait till the doors open
of their own volition at some ritual. You can also take the other way inside through
the front gate where Sherincal is.
Rawel

this is the level 1 fortress where the goblins are

Are you still in the warren under the fortress entrance if so you will need the two ward stones one iron and one is stone to make the gate open. if you don't have the ward stones go search the dead Goblins or go kill the rest of them until you find both of them and the don't loose them until after Chapter two
is well under way. One of the ward stones is on a goblin mage near the cows and corral area.