Is this even do able solo or is there small text somewhere saying be in the biggest group can an some where.
Make a raid and invite a dozen or so people. On your go, everyone runs around the area and you'll get the achievement in about 20 seconds.
I got it on my own, but I had to wait for a server restart to do it. Was right beside the pit and logged on the second my server came up and got it with some time to spare.
Ya i've tried getting a raid no one wants to do it so guess i have to wait for a reset.
I solod it today at like 5am server when no one was around and just waited for a bunch of groups to spawn close together and went for it.