The Temple of Xayepocax is a room deep down in the Edron Hero Cave. It houses a quest and many, many different creatures. This is a great place to try and kill your first Warlock. A good strategy would be to lead him through the entrance's narrow corridor and then trap him in a corner.
In total, this room contains 3 Demon Skeletons, 3 Monks, 3 Hunters, 2 Heroes, 2 Priestesses, 2 Witches, 2 Dark Magicians, 2 Dark Apprentices, an Orc Shaman, a Stalker and a Warlock. Note: they respawn fairly quickly, so be careful.