One that I really enjoyed during my pretentious phase was the father of modern philosophy himself, Immanuel Kant. He wrote a lot about ethics and aesthetics but the crux of his work boils down to the idea that space and time are just "forms of intuition" that structure our experience and are just appearances we can comprehend. The true nature of things as they are in themselves is unknowable to us.

As someone who has always considered themselves very rational and more of an agnostic than an atheist, his ideas really clicked with me.