It's the residual portal from the Praetorian invasion event. I believe they were left in place all Memorial weekend while the badge (Defender of Primal Earth) was still being rewarded for logging in.
That is a portal to Praetoria, a holdover from the big game-wide server invasions the Devs hosted a week back. Seems to have been one portal, or an extra WarWalker or something walking around in zones after the invasion (something to do about helping to cue the event spawns, if I remember right).
EDIT: Huh. Having those in-place for the badge...didn't think about that. Might be it 
Global - @El D
Servers - Protector
I ran across one when I exited a mission and the map/graphics somehow failed to load correctly, leaving only the clouds, doors and windows, people and cars. My character (who was rendered ok otherwise) kept dropping below ground level about 20 feet then popping back to ground level, dropping again, etc. I ended up going around exploring and now wish I hadn't logged off so early and taken more screen shots. Glad to know what this thing is now.
This is now my desktop.
I guess I have been out of the loop for awhile. My guess is that this is a residual porthole from a previous TF or Trial that is new from the last issue update, would that be a correct assumption?
