There are 4 lairs in the Land of the Dead. Each lair requires a different combination of Glyphs to be able to enter. These Glyphs can be unlocked by doing the Land of the Dead Public Quests. When your entire 6 man group has the right set of Glyphs activated, your party leader must zone into the Lair entrance to set the instance ID. After that, the rest of the group can zone in. Note that you can't zone in while in combat. There is also currently a bug where a mob called 'Lair Glyph Effect' will aggro you at the door. If this happens, you can kill it using AoE effects, and zone in as soon as it dies before another respawns to take it's place. Lairs do not have lockout timers. Instead, once the boss is beaten, the glyphs for that lair will darken. In order to do the instance again, you must re-obtain the correct glyphs by re-doing the associated PQs.