Basically what's been said above. Group dungeons, PvP, Wrothgar WB, public dungeons(as opposed to group they're not instanced and can usually easily be soloed, but they do have a lot of mobs so it makes sense to do them with several players)..oh there's also Craglorn. It's an extremely underrated zone in my opinion - it greatly lacks any meaningful reward for doing it, even in terms of exp, but it's still a whole beautiful zone with some extremeley well designed delves/fights etc. You have to be at least vet 1 in order to enter Craglorn and it's been designed as a group zone(though it's been nerfed immensely since then so by now a lot of people can easily solo most of it). There's a couple annoying quests there which require set number of people(up to 4 for a couple quests) to progress, but for the most part you can have great fun there with just a couple of friends if you aren't bothered by lack of meaningful reward.