You come across this large round structure and suddenly 6 figures pop out of the ground, your first reaction may be to attack them right away but doing so will cause all of them to attack you at once, if you're starting out that may be a very unwise decision. It's better to take caution, allow them to take their position next to each other this way you can attack with a group / ground attack striking them all at once. If you feel like there's too many of them initially to take on, don't worry about it as you can wait it out and they will thin themselves out as they get sacrificed to the hole in the sky. Eventually they will go down to just 2 remaining for easy pickings before they return back up to 4 then it cycles between these numbers.

The initial spawn locations are always the same starting with one in the back left and two on the right side of the dolmen for the first wave. If you have ground effects you can lay a couple down to get the drop on them before they get the drop on you. Learn to memorize these positions and their spawn timing to better manage your time spent on taking them down. An increased number of spawns will generate when the player count around them goes up as well. You also want to keep moving around, standing in one place too long causes a negative ground effect to spawn under you dealing constant damage, move every so often to prevent this from happening.

As you kill your way through them you'll notice their souls going into 4 objects around the dolmen, these are called Pinions and they aren't there just for show! Interacting with a Pinion will restore everyone's magicka and stamina to full, so if you find yourself getting low or exhausted on resources do not hesitate to close a Pinion to get a refresher. If you close the 4th Pinion before all the spawn mobs are killed, it will instantly kill the remaining mobs still standing, you'll want to tag them all to get experience credit before doing so. Mobs will eventually stop spawning on their own once all Pinions are filled, a couple of stragglers will still come down but it stops there. If you have companions its best to finish off all the monsters as they get all their experience gains from your kills not from the dolmen objective.

Closing all 4 Pinions will activate the next phase of the dolmen. 2 packs of trash mobs will spawn with one just to the right of the steps, another in the middle of the left side, and a boss generally in the circular area just to the left of the steps. Try to take out the pack of mobs on the right side of the steps first, you can tag the boss then sprint around counter clockwise to get him to follow you while you take out the other trash pack. You can use the dolmen's center to block line of sight from the boss preventing it from attacking you directly if you feel it is too strong for you to handle, taking shots at it from a distance. Once all the mobs and boss are dead, the 5th and final Pinion pops up, close that, get a large experience bonus for completing the objective and collect the chest that spawns to the right of the stairs.

BONUS: If you come across a dolmen that has been completed that you took no part in, but the 5th Pinion has not been closed yet, rush it and try to close it before anyone else. If successful you'll get the objective completion, the experience bonus, and the chest without having to lift a finger in the ordeal leading up to it.