This is the forum for helping you out if you're stuck or if you want to discuss the nitty gritty details of the dungeons within Mount Grimrock. Warning: forum contains spoilers!
The second key is in one huge hall with ugguardians. There is a small button puzzle with traps.
You press the button behind the column to the left run fast to the first trap which closes and press the next button.
Turn left , turn right , right again , press the next button fast , before trap will open and there is an alcove with one round key.
The other traps are for nothing you don't need to close them.
----
But you need 3 to pass the level and 4 to open and one iron door , but I cant find the forth.
The third key exist in one portal which transfer you in some places very fast and you need to step fast to get out from the portal.
The portal travels you fast in some places , if you stay in the same square , when you kill some scorpions will take the third round key from one alcove.
SpoilerShow
I don't know where is the forth key , the forth key is only for the iron door , not important for the progress of the game