Take a moment to breathe a sigh of relief and satisfaction before this movie begins. You’re in good hands. And enjoy that breath because it may be your last for the next three hours.

One of the most ambitious projects in the history of film-making comes to a heart-poundingly thrilling conclusion in “Return of the King,” the last episode in Tolkien’s Lord of the Rings trilogy directed by Peter Jackson.

The second installment opened in the middle of the action, but this one begins with a flashback. It’s not there to repeat anything we’ve seen before — there’s no time for that. This glimpse of the past is just to tell us something more about Gollum, the twisted, tortured creature who is supposed to be leading Frodo (Elijah Wood) and Samwise Gamgee (Sean Astin) to Mount Doom. It is also there to tell us more about the power of that ring to make anyone willing to give up all he has to possess it.

After that very brief prologue, we are back where we left off, a literal cliff-hanger. Frodo, Sam, and Golum are crossing the stark peaks on the way to the volcano in the heart of Mount Doom. That is where the ring was forged and the only place where it can be destroyed. Meanwhile, the other remaining members of the Fellowship of the Ring prepare for battle with the forces led by Sauron.

As with the first two chapters, Peter Jackson’s rendition of the J.R.R. Tolkien classics is astonishingly inventive and new and yet so clearly right that it seems as though it always existed inside us. Every detail is just right, from the leaf-shaped clasps on the rough wool cloaks to the huge mumakils, mastodon-like creatures carrying Haradim warriors in vast contraptions that look like masted schooners.

And from the struggles of three very small creatures to stay alive as they scale sheer rock to the huge battles with hundreds of thousands of warriors, Jackson makes every moment vivid, exciting, and moving, filling every frame with wonders. That means not just Middle earth citadels, a giant spider, a battering ram that is an ironwork boar filled with fire, and thousands of phantom combatants, but also smaller moments of equal power. Sam and Gollum each try to make Frodo mistrust the other. The steward eats alone at his table, bright red juice dripping down his chin, as his son leads men into a doomed battle.

There are villains, grotesque and powerrful, weak and greedy. And there are heroes, loyal, brave, devoted, honorable. Told that death is certain and there is small chance of success, one replies, “What are we waiting for?” Who needs to breathe when there is all this to see?

The tone is epic and majestic, the battles brilliantly staged, the vistas magnificently conceived. But it is still all about the story. Characters learn and deepen. Even little Pippin and Merry go from cute comic relief to genuine heroes.

There is so much going on that some characters feel like not much more than cameo guest appearances, especially Arwen (Liv Tyler) and Galadriel (Cate Blanchette). And the post-ending endings, after more than three hours, may seem a bit too much. But this is still an epic to satisfy the most devoted fans of the books and viewers who are new to Middle Earth. In its own way, it is as thrilling an adventure in story-telling on film as the quest it portrays.

Parents should know that the movie has intense battle violence, graphic for a PG-13. Characters are injured and killed. While there is no modern-day profanity, characters use some strong language. A strength of the movie is the way its diverse characters learn to trust each other and work together. Some critics have accused the original books of racism, with dark-skinned, slant-eyed bad guys fighting pale-skinned good guys. But there is no evidence of any such intent, even unconscious, in Tolkien’s work or in this movie.

Families who see this movie should talk about what it was that made Frodo more resistant to the evil pull of the ring than anyone else. How are Frodo and Aragorn alike and how are they different? Why did Frodo and Sam make different choices at the end? What is the answer to the question, “Why should we ride to the aid of those who did not come to ours?” Why? What is the role of choice and what is the role of fate in this story? Why can’t Gandalf just use his powers to make sure the good guys win? Who surprised you by doing more than you thought they could? Who surprised themselves?

Families who enjoy this movie might want to look at pictures of some of the real-life creatures that inspired those in this story, including pterodactyls and mastodons. And every family will enjoy reading aloud the entire trilogy, or listening to it on the superb BBC audio edition.