Hi! Our congrats for getting all stars on nightmare. That's definitely not easy achievement)
The giant bell currently cannot be activated but it will be able in the future updates.
And yes, some of the screenshots are from deeper tiers of the dungeon which is not included in the current demo. But those tiers will be available on Early Access release.
BTW We released a big update several days ago. So you are welcome to try it :)
Thank you!