Welcome to purgatory, brought to you in black and white.

The great Willem Dafoe and the impressively versatile Robert Pattinson stage a two-man horror show for the ages in Robert Eggers’ “The Lighthouse,” a claustrophobic nightmare symphony of often cringe-inducing sights and sounds.

At times, it feels as if a more appropriate title for this film would be “The Outhouse.”

But this truly IS must-see cinema — one of the most visually striking films you’ll ever see, featuring magnificent performances from the two leads.

Dafoe goes bigger and bolder in his work, but Pattinson has his moments of screen-filling madness, as well. They’re equally brilliant.

“The Lighthouse” is set in the late 19th century, but it really does feel more like we’re immersed in some sort of between-two-worlds, suspended state of existence.

Pattinson plays a young drifter named Winslow, who has contracted for a monthlong gig on an isolated, storm-swept island as an apprentice for crabby old lighthouse keeper Thomas Wake (Dafoe), who is given to barking orders, riding Winslow as if the guy is a prisoner doing hard labor — and filling the air with flatulence.

Yes, he’s quite a guy.

Winslow and Wake are practically on top of each other for the duration. In addition to the lighthouse, there’s only a signal house containing the foghorn, and a small cabin where they have to sleep, share meals and co-exist.

Director Eggers (“The Witch”) and the cinematographer Jarin Blaschke shoot “The Lighthouse” in a nearly square aspect ratio, further deepening the sense of claustrophobia. When we venture outside with Winslow and/or Wake and the camera pulls back, there’s still something suffocating about the visuals. We have a palpable sense of how Winslow feels as he regards the horizon or looks up and sees the increasingly deranged Wake up in the lighthouse.

He’s trapped. He might never get out of here.

Winslow tries to stay out of Wake’s path as much as possible, but that’s physically impossible in these surroundings, and the two men are forced into a kind of warped friendship, fueled by nightly drinking binges, revelations of deep secrets, fierce arguments — and a power dynamic that could be shifting.

With his angular visage and his roaring line deliveries, Dafoe is like a villain in a graphic novel come to life. The sadistic, sometimes incoherent, drunken Wake is a waking nightmare for Winslow, who has his own problems, what with being convinced he’s met an actual mermaid that has washed ashore.

If all this sounds crazy, it is. “The Lighthouse” is a descent into madness. But the journey is often surprisingly funny, as well.

We end up having a much better time than those two miserable wretches stuck with each other in the dead-center middle of nowhere.