User blog comment:Timeoin/Tamriel Unlimited gets its first official DLC/@comment-62.1.170.116-20150719115333/@comment-1600847-20150720165235

... except Trials, Group Dungeons, and Adventure Zones. Used to be you could solo Group Dungeons, but with level-scaling it's now impossible.

Zone Bosses, Dark Anchors and Public Dungeons are tougher to do solo, but still possible.