To set your film entirely in one room is to risk being visually boring. How do you avoid stagnation when there’s a limited number of different angles to shoot from? Usually we’re obliged to focus on the story and dialogue and accept that there won’t be much to stimulate the eyes. When a filmmaker finds a way to keep it fresh in spite of the claustrophobia — like Sidney Lumet did in the jury room of “Twelve Angry Men” — it’s noteworthy.

So major kudos are in order for Spanish director Rodrigo Cortés, whose second feature, “Buried,” is set in a coffin — about as small a location as you could have for a movie about a normal-sized human. Yet Cortés and his cinematographer, Eduard Grau (who also did outstanding work on “A Single Man”), find an impressive number of ways to keep things fresh without resorting to gimmicks or tricks. It’s sheer technical skill at play here.

The coffin is occupied by Ryan Reynolds, essentially the only actor in the film and deserving of praise for holding our attention single-handedly. Not everyone can do that. He plays Paul Conroy, a civilian contractor in Iraq who was driving a supply truck when insurgents attacked and he lost consciousness. Now he wakes up in a coffin — a fairly roomy one, as coffins go, but a coffin nonetheless — apparently buried in the ground. He has a cigarette lighter, a pen, and a cell phone with him, the latter provided by his abductors, who use it to contact him and give him their ransom instructions.

And that’s basically it. To say more about the story — indeed, to say whether there even IS more to the story — would be unfair. Without giving anything away, I can report that the film stays on the road of the mostly plausible. If you can accept the outstanding cell phone reception Paul gets underground (he’s probably only a couple feet down) and the unlimited oxygen supply, the rest of what transpires is, pardon the expression, down to earth: no supernatural elements, no outrageous plot twists.

Now, whether that’s good or bad is a matter of opinion. I appreciate that the film takes the scenario of being buried alive and lets it play out logically, but part of me thinks the movie (which was written by Chris Sparling) might have been more satisfying if it had taken a more imaginative route — if it had been a little less realistic, in other words. When it’s done, you think, “That’s it?” But then you think, “Well, but what else COULD have happened?” This might be as good a movie as could have been made with this premise.

I can’t overstate the film’s technical merits — the camera angles, the lighting, the editing, the musical score, they all contribute to boosting the energy and suspense of what could easily have been a dull 90 minutes. Reynolds expertly conveys the frustration, fear, and anger of the situation, keeping us with him every step of the way. You probably have never seen a movie like this before, and if it’s not completely successful at least it makes a respectably entertaining attempt.

B (1 hr., 34 min.; R, some harsh profanity, brief strong violence.)