Nobody knows, it's impossible to imagine. That's the point. It's all fancy talk. To elaborate: It's where geometry beyond human comprehension exists; angles intersect at impossible angles, and colours from outer space blend into shapes that are detrimental to your very sanity. I think the closest possible analogue is to take 10 grams of shrooms and then smoke a fuckton of weed to land yourself in a bad trip with ego-death where you're falling through fractal patterns while losing all sensations of yourself. You will not know who 'you' are anymore, and feel like you are going insane with extreme fear, but you cannot even grasp the very concepts of fear or sanity; yet you realize something is terribly wrong.