The vault has a whole level. You _can't_ miss it unless you're purposefully trying to. When walking through the level the map showing the secret entrance is right there on the floor.
I missed Nex the first time I did the puzzle, got it after I ran through the level again trying to find secrets. If I wasn't a munchkin I'd never have gotten it.
Going past a switch which closes a trapdoor (though seemingly for no reason) is very easy, going past an entire level you can't enter, with a prominent clue as to how to do so on the floor, not so much.
But yeah. Whatever. I think it's fine too, looks cool
