In Flyff Universe, there are now instanced dungeons where you can go in with yourself or a party to defeat all the monsters within.
It can be quite confusing to get in.
Unlike the Mars Dungeon where you can just go into the cave outside and you’ll get automatically warped in, you need to talk to the NPC in front of the Leren Chasm.
Click on the Leren Chasm Guard, then click on Dungeon. Once you do that, you will see the following window:
At this point, you can pick the correct option to start completing quests or get items.
If you would like to just complete the Leren Chasm Guard general quest, pick Leren Chasm (Story) mode.
Good luck!