You have probably came across several hidden locations in Guild Wars 2, but this one is worth mentioning because there are already implemented some cool features. According to the latest rumor, a creepy rooms could be some kind of riddle maze in the future. It’s located in Caudecus’s Manor instance, and you need a blink ability to get inside.
Important Note: Unfortunately the original video has been removed. I found the second one that leads to the same location.