The Fort Rotulor dungeon is the first one you will gain access to and takes place inside a large cathedral-like structure, reminiscent of a castle throne room. The area consists of a large central floor-space and a slightly elevated section to either side of the central space, and a raised altar at the end. There are creatures scattered throughout the central and side areas, along with one required boss in the central area, one optional boss on the right side that appears if you talk to the human soldier there (needed for at least one quest), and the final boss appears at the end altar soon after the boss in the central area is defeated. This has a pretty standard goal: kill everything, aiming to leave the bosses for last.
There is a special Achievement for this instance which requires that you beat it within 5 minutes. You will need a strong party of lvl 40+ players to do this, and at that level the Fort will not appear as an option for you to join from the T menu. However, you can still approach the Fort in the Kalaires Plains and apply for it manually there. The way to get this achievement is to simply charge straight into the central area and attack the first required boss, killing him as fast as possible and ignoring everything else that attacks you, and then charge up to the final alter to attack and kill the last boss. However, be advised: The instant you attack the final boss, everything in the room is going to come charging at you hard, and even though they are lower level creatures that damage can build up quite quickly in those numbers, and they are significantly tougher to kill than normal lvl 15 creatures. You are going to need at least one good priest and three mages to kill everything fast enough, as well as a good supply of potions.