I'd all the Southern Reach trilogy (quadrilogy? now) to this list. It's more on the cosmic/eldritch side, but similar sense of unknowable.

SPOILER WARNING

My interruption is that Area X/The Crawler is a probe built to study and build a bridge back to its creator. Area X is expanding because it's the inside of a wormhole. But whatever is on the other side is long dead, and the probe is acting on instinct.