I was just thinking about a new item for a portal 2 level. Imagine if as the player falls down a pit fling they pass through a ring and come out in another room. Or maybe they are flinging across a chasm and they pass through a ring coming out in another room. The ring would obviously be a world portal, but the idea is that the portal would be "floating" in midair. It would appear as if from nowhere.

I think its possible, but I don't use world portals because it is very hard and time consuming sizing them

I don't really think that work portals are difficult to scale. You just make a brush the size you want it to be, look at the dimensions, and divide them by 2 and punch those into the world portal entity. Takes about 1 minute

uh so thats what you had to do -' I manually sized them.

I was referring to something that behaves like a Star Gate. The difference is that this "floating" portal would pop out of nowhere. Granted there have been levels that utilize a circular frame in the middle of the room. Those levels, however, have the portal activated by some visible switch or button. I imagined the portal appearing in the middle of a hallway as if by magic. it would freak out the player somethin' fierce and be damn funny for the designer.