A famous astronomer, Johann Zöllner, came up with a number of different tests designed to show that a person has the power to go into four-dimensional space. See if you can pass one!
In this obscure Jack Kirby strip from 1957's Alarming Tales 1, a man chases a burglar into a geometric hellhole, where he falls in love. It's a priceless, wondrously nonsensical example of Kirby's pre-Marvel work.
I always thought 4D was time, but according to the fashionable people at Ralph Lauren, 4D is actually perfume wafting out of huge projected-upon stores. Even if you're dressed in hoody and jeans, you'll still find this quite impressive.