Describe your BBEG demiplane

[flappeercraft]

So right now I just randomly want to actually make use of a demiplane for the BBEG of a campaign I'm running so I wanted to know what kind of things would your BBEG's demiplane have as inspiration on what to add.

[noob]

It would use gravity to kill intruders unless they stay on a stone path.
Nearby there would be a panel with written "warning weaponized gravity" hoping it would convince the adventurers to stray away from the path.
Oh of course the precious stuff I would keep would not be linked to that path I would just use a spell to protect myself from gravity or the plane have as a trait that the weaponized gravity do not works on me.
meanwhile I would have armies of undead haunt shifted in the path so that the adventurers believe there is stuff to do here(and even levers and buttons which are connected to a coffee machine except that it would be very hard to find that out hoping the adventurers believe there is stuff to do with those buttons that advance their quest).
There would also be spell turrets everywhere shooting at intruders and possibly some secret super hard to reach passage leading to a room with one single lich phylactery except it would not be mine.
The actual stuff that matters for me would be in another plane I reach by planeshifting from that place from a location in that plane that nobody can get to unless they are immune to weaponized gravity, heat superior to the one of the sun and constant peppering by spell turrets and some other defences(of course there is antimagic zones and anti-teleport zones that does affects everybody except me since I get to pick the traits of the plane) all that is so that the second plane shift is very hard to trace.