For example, Jerry counts as he swims: "[A] hundred and fifteen, a hundred and fifteen pounded through his head," higher numbers than he has counted in his practice sessions. These high numbers create tension as the reader has known that Jerry has not counted holding his breadth this long before.

Other words and phrases that convey tension and danger are those such as "His head was swelling, his lungs cracking"; "His hands, groping forward, met nothing; and "his feet, kicking back, propelled him out to the sea." Further, when Jerry is "gasping" and "a gout of blood" passes into the sea and he knows that his nose has been bleeding, there is anxiety created in the reader that Jerry may have injured his lungs.

Clearly, Doris Lessing's diction and style of description draw the reader into the narrative as suspense and tension is created, lending much verisimilitude to the passages about Jerry's attempts to swim under water for a long stretch as well as his final attempt to pass through the tunnel as the older boys have done and complete his rite of passage. 

Word choice is an instrumental technique that Lessing employs in "Through the Tunnel" to heighten the suspenseful mood of the story.

Although the action is set on a beach, the area where Jerry dives is portrayed as anything but the safe and relaxing beach where his mother rests. While her beach is safe enough for young children, the word choice used to depict the area of the cave is ominous. There are "inlets of rough, sharp rock," and the "rocks lay like discolored monsters under the surface." He watches the group of boys dive "between rough, pointed rocks," and after they leave him, Jerry sits on the diving rock and feels the "hot roughness of it under his thighs." When Jerry finds the spot which contains the tunnel, he compares the area to an "anchor of stone" and describes the tunnel as an "irregular, dark gap; but he could not see deep into it."

Jerry uses this opportunity to separate himself from his mother's protective reach, and he is willing to face the wild and dangerous aspects of nature in order to prove himself capable of independence. The word choice in the story establishes the particular dangers of this independence, and those efforts are filled with blood loss as Jerry battles the sea and rocks to achieve his goal. The word choice describing his setting conveys the seriousness of Jerry's intentions and the inherent dangers involved in emerging from childhood and entering a world full of wildly dangerous possibilities.

On the surface, one might assume that this is a story about a young boy's beach vacation with his mother as he is on the cusp of manhood. But Lessing quickly draws a distinction between the "wild bay" and the "safe beach" described at the end of the first paragraph. When Jerry gets to go to the "wild bay" without his mother, the narrator describes how he must run "sliding and scraping" over the "rough, sharp rock[s]" leading to the water. The surface of the water shows "stains of purple and darker blue" (which sound like bruises) and in the water itself, "rocks lay like discolored monsters." These descriptions help to convey the setting of Jerry's underwater exploits in the wild bay and the negative—even dangerous—connotations of the words used also convey the mood of the story as well.

The "safe beach," however, seems so innocent and childish. Jerry looks back from his bay at his mother: "There she was, a speck of yellow under an umbrella that looked like a slice of orange peel." This description connotes such positivity, the kind of details we expect from a beach vacation: bright colors and citrus fruits. Descriptions like these allow us to understand the two beaches as they are juxtaposed—how they are different and why Jerry would prefer one to another.

One thing interesting about the setting in the short story "Through the Tunnel" is that author Doris Lessing carefully uses word choices to show the striking contrast between the beach and the enticing rocky bay, and the contrast helps set the mood of the story and develop the major theme.

In the beginning of the story, "the young English" boy does not show very much enthusiasm about taking the same vacation as usual with his mother. However, he begins to get interested when, walking along the path to the beach, his mother in front of him, he looks "down at a wild and rocky bay." Lessing's use of the term "wild" to describe the bay setting creates tension. We clearly see that the boy is captivated by the sight of the bay but also sense the bay may not be entirely safe. In addition, the term "rocky" helps to capture the rough surface of the bay, which further helps to characterize the bay as not being the safest area in the world.
In contrast to the "wild and rocky bay," the boy is heading with his mother towards the "crowded beach" he has already been familiar with for years now. As he follows his mother, he notes that she is "carrying a bright striped bag." Lessing's use of the word "crowded" helps to capture the civility of the beach. If it is crowded, it is obviously popular, and popular beaches contain nice, smooth sand and refreshing water that captivate society's civilized people. In addition, the adjectives "bright" and "striped" capture the cheerfulness and festivity that are characteristic of beach vacations.

However, the boy is not interested in civilization, brightness, or cheerfulness. Instead, he is interested in something new, exciting and adventurous. Hence, Lessing contrasts the description of the rocky bay setting with the crowded beach setting to establish the mood of the story and to foreshadow the dangerous adventures the boy is about to undertake. Plus, though his adventures threaten his health and life, they also show his maturity, which establishes the coming of age theme in the short story.

Doris Lessing is very adept at conveying a setting through the use of few, carefully chosen words. In this story, we can see this skill at work. She describes the bay, for example, as "wild and rocky," two descriptors which immediately help us to understand that this is not a place where it is safe for children to bathe, but a cove where the tides crash in fiercely and where a person could easily be injured by the unpredictable sea. Likewise, the beach adjacent is "crowded"—putting these two elements together, we can interpret that the reason the beach is so crowded is because the bay area is not available for bathers; it is not a place where people would gather. The word "wild" is not used only once, either—in fact, Lessing uses it twice within the first couple of paragraphs in her story, emphasizing the fact that this is what she wants the reader to remember about the bay.

Word choices that convey the story's setting -- in fact the two different settings -- include the "wild bay" and the "safe beach."  We know, right away, that we are in a beachy, vacation setting based on words like "shore" and "holiday"; further, Jerry focuses on the swinging of his mother's "white, naked arm" and how she carries her "bright-striped bag" and, later, how she sits under her beach umbrella that "looked like a slice or orange peel."  Moreover, the narrator's descriptions of the wild bay and its unpredictability help to convey the sense of danger in this setting.  It has "rough, sharp rock" with water that "showed stains of purple and darker blue."  Even more notable are the description of rocks that lay on the ocean bottom as "discolored monsters" and the mentions of "irregular cold currents" that "shocked [Jerry's] limbs."  The water is a "solid, heavy blue," letting us know that the setting is, indeed, a large body of water.

I think the atmosphere and mood that is created through those words is a suspenseful, tense, and ominous atmosphere.  Dorris Lessing needed to use words like "dark" and "looming" in order to change the initial atmosphere of the story.   The story starts out with a mother and her son on vacation.  They are staying at some kind of beach resort.  Beach resort and vacation.  That immediately creates a relaxed and happy atmosphere for the reader.  

Lessing changes the mood of the piece after Jerry goes out on his own to the wild beach.  Once that happens, Lessing uses the word "dark" frequently.  

He could see the hole. It was an irregular, dark gap; but he could not see deep into it.

She uses it to describe visibility through the water.  She uses it to describe the hole itself.  Lessing also uses words that are descriptors of large items -- "big, heavy, looming," etc.  All of those word choices together alert the reader to the presence of danger despite the relaxed vacation atmosphere.  Doing things that are dangerous create apprehension in people.  There is an ominous atmosphere about those actions, because there is always the risk of failure.  Lessing's word choices help cement the danger and ominous overtones in the reader's mind about what Jerry is going to attempt.  

In the first sentence, the narrator tells us that we are at the "shore" and that the "young English boy" and his mother are on "holiday."  Thus, we can begin to ascertain that the setting of the story is the seaside, and mother and son have gone to the beach for a vacation.  Later, when Jerry is trying to fit in with the older boys who are able to swim through the tunnel in the rock at the wild bay, the narrator tells us that the boys were "of that coast," and Jerry tries to throw all the French he knows at them in an attempt to keep their attention on him.  These are good clues that the setting is, more specifically, the French Riviera, a popular beach locale for British vacationers.  Moreover, the narrator draws a distinction between Jerry's mother's "safe beach" and the "wild bay" he prefers to go to because he seems to be growing up and desiring more independence than he used to.