In Stormblood, FFXIV introduced a new area/system called Eureka. It's meant to be a more old-school group mob-grinding experience with a lot of players (up to 144 per instance). As such, it's pretty controversial, especially among the forum community which prizes "skill". I kind of like it though.
In Eureka, you have a separate "elemental" level and all your stats are synced to a fixed point. Creatures generally require a group to kill, and experience has a very high drop-off, so you're sort of restricted to a band within two levels of your own. The larger and more skilled your group, the higher you can go.
The mob density is somewhat high. You can sneak around and run behind high level monsters without aggroing them, but you have to be careful and deliberate. If you accidentally aggro a monster with a much higher level, it will kill you in one or two hits. You cannot use a mount until max elemental level.
There's also a mechanic where you can attune yourself to certain elements, and either take less damage from or deal more damage to creatures of that type. Finally, when you kill a creature your level or higher, it starts an "XP chain", increasing the amount of XP you get. If you kill the next creature within a minute or so, the XP chain increases.
So the base way you play Eureka is get into a small group and chain-pull specific mobs around your level. As your level increases, you have to keep moving to find new mobs. There are challenge logs which require you to kill 30 or 60 creatures of a specific element once a week for a lot of XP.
The second way to play Eureka is the Notorious Monster train. If you kill enough of a certain monster, a Notorious Monster will appear. Once an NM is killed it won't respawn for a couple of hours. So people form a train of multiple 8-man groups, and move from area to area triggering NMs.
Killing NMs usually gives more currency to upgrade gear, while challenge logs are faster to level.
There are some interesting design decisions here and there. For example, if you respawn when you die, you lose XP, even dropping you back to the previous level. But if someone resurrects you, then you don't lose anything. So you'll see people asking for resses in general chat, and healers and red mages sneaking around trying to get to them and resurrect. A small binding together of community.
Eureka is not high skill or anything, but I find it fun. It's nice to join a group and just grind, or run around in a large group attacking, healing, ressing, with some chatter. It's low intensity group content, which I think has been missing from the current generation of MMOs. It's something you can dip in and out of. Join the train, kill a few NMs, then leave. Groups pick up new members and lose old members as time goes on. A feeling of continuous content rather than something with a defined start and end.