The Obelisk of Akzul is a group instance from the Shadow Odyssey era. It is originally designed for groups at around level 80, but most people should be able to solo it at level 90+ or with a mercenary. You can do this instance once per day per character and it is a real plat mine so i try to do it every day.
To get to the Obelisk, head over to the Moors of Ykesha. And the instance is a short flight east from where you enter. You should be able to almost see it from the zone in. Once you are inside start clearing all the trash. Once you have killed the trash mobs in the first room you will be able to go to the second room. I like to kill all the mobs here as well to get the boss to spawn but this is not necessary. This room also usually have 3 + shinys that can be worth quite a bit. When you are finished, head through the corridor to the next room. The boss here “Kierax the Energy Wielder” is where you will get your plat. Jump out into the middle of the room and you will start floating about. The key to this fight is to absorb all the orbs that appear before Kierax does. If he gets the orbs, he will aoe you and you will die not matter what level you are. When you have killed Kierax, loot his chest and get about 10 plat.
Now you can choose to either leave and come back the next day or with another character. Or you can finish up the dungeon and try to get some more shinys and maybe some masters from the bosses. All in all it is possible to make 20 – 50 plat in here since the collectable shinys can be worth quite a bit.