Grimrock

I hate to admit it but I am stuck. I need your help in the "maze of madness". I managed to get through the portal maze until the far end of the room. There I enter the left portal (from starting point of view) and I am ported to the right side. I can see a key in the alcove, but whatever portal I enter, I can not reach there. What am I doing wrong ? - Thanks for your help !

OK I got it !

SPOILER:

There is a switch on the wall that will disable the portal in front of the key !