The Ruins of Lxanvom or the Crypt of Decay, is a Planes of Power era zone that can easily be accessed from the Plane of Tranquility. The entrance is in the upper eastern corner of the Plane of Tranquility. You can make a lot of plat here fast, but you should be pretty high level to solo here efficiently. Optimally you want everything to be greyed out so you can blast through the zone and AoE the mobs. If you have everything greyed out though you can pull MASS amounts of mobs and kill them very fast and hardly take any damage at all. If you don’t have AoE capabilities yourself, be sure to bring a AoE mercenary.
The mobs here drop a lot of tradeskill items that can sell for a lot of plat on the Bazaar, plus gems and vendor items. There are vendors right outside in the buildings in Plane of Tranquility so you can go outside an vendor every so often. If you are a F2P member you can make a good amount of gold here but gold members can make 20k + platinum in here.