The latest PCGamer has an article about the high level dungeon near the Sylvari starting area. Obviously I can't scan the pages and post them here, but if you are interested, the May 2012 Issue 226 has it. But I'll share some of the interesting details.
-Level 50 dungeon focused on fighting the Nightmare Court with Caithe at your side.
-Trash mobs have unique elements, archers have a shot that if it isn't interrupted could get you flung into the abyss behind you
-Each boss in story mode is based on an emotion. Sariel, knight of remorse, will pick a single target and focus on them relentlessly. Graingor, knight of horror, uses fear effects on his island in the middle of a huge lake. Catiern, knight of envy, is a Mesmer that focuses on illusions.
-Explorable mode has three paths to choose from that feature more Sylvari that are rising up to fill the void that you created from killing everything in Story mode.
-There are about 10 random events that happen in a dungeon every time you run it. Which could be something like a hidden chest or a giant troll that will ambush you along a path that may have been clear last time you ran the dungeon.
-There is a room filled with plant cannons, which you'll need to figure out the pattern to get past them. If two plant cannons spot you, you're done. There are other traps similar to what we've seen elsewhere, like fire traps and landmines.
-There is a cave with a lake so large that if you ran the outside edges all the way around, it would take you five to ten minutes. Three islands in the lake which house Sariel and other mobs. The lake is huge underwater and could take up to an hour to fully explore. Random encounters/rewards in the lake, like a huge fish mini-boss that will try to eat you.