You're going to need atleast 8 people before you're allowed inside (to search for two more parties of 8), but you can duty finder for it apparently. Still means finishing the "Legacy of Allag" quest first. After that, Duty Finder it up.
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[XI] Surivere of Valefor
[XIV] Sir Surian Bedivere of Behemoth
http://na.finalfantasyxiv.com/lodestone/character/2401553/