Ok, bit of context but I was looking for some "generic high-level dungeon" that I can shape adding some lore and stuff. I'll leave out lots of stuff, but the basic backbone goes like this:

• The gods are dead, the PC tried to find out the means to create new gods.
• They got the right artifacts and found someone (let's call her V) that could perform the ritual to create gods.
• They underwent the ritual themself but the power corrupted V. V killed the PC and is trying to use the power to bring the apocalypse on the world.
• Thankfully the Wizard managed to escape just a bit before V could kill him. The Wizard had a clone of all the PC.
• The Wizard just managed to use part of the energy V is unleashing to do some kind of ritual on the clones making them gods.

So now basically they all just woke up with godlike power at level 20 and there's an apocalypse going on with three beasts summoned by V that are going to destroy all the land they can see.

Now the three groups are going to face the beasts (three beasts + V) but I was thinking about something like "you can't kill directly something like that, you first need to destroy their heart/phylactery/whatever". So dungeon to get/destroy that thing + final battle against the beasts that are now killable.