>>274794027
You unlock the sandbox by throwing all of the items into the archive bin at the start of the game, then pushing open the door to the Archival room in the museum, which is locked otherwise. There's a boneworks box there with a module inside of it. Take the module through the level and throw it into the recycling field next to the vending machine. Buy a nullbody capsule while you're there and toss that in as well.

You can only spawn things that you've thrown into recyclers so it's kind of disappointing.