Lava Mountain is the huge volcano found West of the Badlands. To access this area one must have P2P, as well as either Lava Boots, (and preferrably Mountain Boots,) which can be obtained from a Travel Store, or Travel Boots. As in the badlands, PvP is possible, here.
One of the main reasons why players come to Lava Mountain is to get Rare Items. The first RARE item is found by killing Demons of either kind. They are sunglasses. These are popular because of their rarity and the way they look.
Lava Helms used to be dropped by Lesser Demons, and Greater Demons dropped Lava Shields before Living Darkness was discovered with Death inside. The chances of getting sunglasses were also half what they are now.