To enter this zone you need to speak to the NPC outside of the entrance. After doing so, you will be able to enter.
There is one encounter, with no trash to clear, like most T5 instances. If you do not kill the eyeball, Overlord Oxulius before killing the stroke victim, Pkwkz Tzkr (Sentinel race NPC), the Overlord will begin a script calling for the help of Borxx, Broxx, Bixx, Brixx, whatever their names are; the contested encounter at the bottom of OoLS.
As of September 2015 there is absolutely no point in letting the Borxx encounter spawn. This extra encounter used to drop an additional chest, that is no longer the case. Currently, it's completely bugged out and spawns two copies of the encounter, resulting in 8 mobs total. Don't bother trying to get loot or be a good raider, just do it the boring way and get your treasured chest. Oh, because T5 loot sucks.