The raid version of Kharazan released many, many years ago during The Burning Crusade expansion, and while the majority of the content from that era has become either outdated or outright annoying (leveling through Hellfire Peninsula anyone?) Kharazan has remained just as unique as it ever was. Everything from the boss design, to the overall atmosphere, to the few bits of voice acting found throughout the raid - all of it still remains within the collective memory of the WoW playerbase, while most of the other raids from that era have long since been forgotten.
If you need any proof for all of these claims, look no further than the next patch coming to World of Warcraft: Legion as it will be bringing with it Kharazan as a five man Mythic dungeon. If you don't feel like waiting for the patch to slowly arrive, I do have some good news, its currently available on the PTR (Public Test Realm)! So if you feel like reliving the glory days of Kharazan before everyone else - now's your chance! On the other hand, if you're a brand new player and have no idea what Kharazan even is, worry not as Blizzard has also released a brief preview video to hopefully get you acclimated. Have a look:
Before I let you loose upon the ancient halls of Kharazan there is one bit of information you should know first. The entrance to the new dungeon is on the side of the tower, accessed via an elevated bridge on the right. Walking through the front door will simply bring you into the old school raid version of Kharazan, which while exciting might not be exactly what you were hoping to test out during this PTR.
Have fun, and if you have any feedback to report make sure to use this thread!