IIRC AC has a secret room full of turkeys. (I think its AC anyway)

The lake and the pillars in a cave in AC. There are invisible walkways between the pillars like in Indiana Jones and the Last Crusade. And then there's some scaffolding on the far side of the room you can jump halfway up.

Has anyone else noticed the owl and raccoon that seem to walk around together in Queensdale?

What about that hidden waterfall in the grove?

I found a secret room in Sparkfly Fen near the Vista at the west side, an old ruin temple with some ooze's, really nice place, but no pratical use.

Ended up underneath one of the lodges in Hoelbrak once. The floors are transparent from underneath....

I managed to get down to the bottom of Rata Sum (inside) the other day. Not much down there but it was cool anyway. I also really like the hidden area in north east of the bottom level of The Grove. I found it during Beta almost by accident and I still like to go back there sometimes just because it looks nice.

Go to the jumping puzzle in the middle of the WvWvW map. as soon as you enter and you're on the platform, there's a hidden area (i think through a wall i cant remember) at the back and you can fall down into this blank room. only way back up is with mesmer portal. i think its a glitch, not sure if fixed yet.