There are crypts and caves to explore. They aren't very complex. You can complete them and not get lost even without mapping on paper or using an AP. The game can be played cooperatively. I am playing a game on a server with 3 other players. We have player damage turned off and share resources and every time one of us builds a new outpost we make sure that there are 4 beds and a portal that leads to one of our portal hubs. There are no quests per se. Ravens give you information and there are bosses to kill that unlock events and items. The game feels much more like a sand box than a quest or story driven game.

Originally posted by Guh~hey~hey~♫:

No man's sky....

No Man's Sky's multiplayer was added as an afterthought. Its still got bugs in it after all these years and even when you are playing coop its more like soloing at the same time and in the same place. Weather doesn't sync, ship and pirate battles don't sync, and resources can duplicate or disappear because multiplayer doesn't sync.

I have over 1,500 hours on No Man's Sky and don't recommend it for multiplayer for anything other than the Expeditions.

If you want a multiplayer sandbox where you can have literally hundreds of players either coop or PVP Factorio is a good one. The only issue with it is that is a 3D emulator in 2D. There is a free demo you can download and play to see if you like it before you commit to buying it.