Setonaikai National Park

Stand near the water on a calm morning and listen. There is almost no surf here. The sea moves in soft folds, and the air carries salt, diesel from a passing ferry, and sometimes the faint sweetness of pine. Out in the haze, low green islands sit one behind another, each a little paler than the last. This is the Seto Inland Sea, and the protected landscape around it is called Setonaikai National Park.

The name itself is simple. Seto means a narrow strait. Naikai means inland sea. Together they describe a long body of salt water held between three of Japan's main islands: Honshu to the north, Shikoku to the south, and Kyushu to the west. Osaka sits near the eastern end of this sea. For centuries, its harbours were the place where goods and travellers from the west arrived at the edge of the old capital region.

Here is the first surprise for many visitors. This is not a single park with a gate and a fence. It is one of the largest national parks in Japan, and it stretches across many prefectures, from the Osaka and Wakayama area in the east to Fukuoka and Oita in the far west. Most of it is water. The protected land is scattered in pieces: headlands, mountain viewpoints, beaches, and island after island.

And those islands are the heart of it. People usually say the Inland Sea holds around three thousand of them, though the exact number depends on what you count as an island. Some are large enough for towns, schools and farms. Others are little more than a rock with a few twisted pines on top. From a high point, they overlap like layers of painted paper — the view that Japanese artists have returned to again and again.

The park also has a place in Japanese history. In 1934, Japan created its very first national parks, and Setonaikai was one of that first small group. At the time, the country was trying to define which landscapes it considered truly national treasures. The choice says a lot. It was not a wild, empty mountain range. It was a lived-in sea, with fishing villages, shrines, terraced fields and boats.

That human layer is the second thing many visitors miss. This sea was a highway long before there were trains. Rice, salt, timber and pottery moved along it by boat. Merchants, monks and officials sailed between its ports. Small harbour towns grew up in sheltered coves, where ships waited for the right tide and the right wind. Some of those towns still keep old wooden warehouses and stone steps leading down to the water.

Tides matter here more than you might expect. Because the sea is squeezed through narrow channels between islands, the water can race in surprising ways. The most famous example is in the Naruto Strait, between Awaji Island and Shikoku, where strong tidal currents form whirlpools. Sightseeing boats go out to watch them churn. It is a reminder that this calm-looking sea has real power beneath the surface.

The climate shapes the mood of the place too. The Inland Sea region is known for mild weather and relatively little rain compared with much of Japan, because the mountains on either side block many storms. That is one reason the coast became home to salt making, citrus groves and olive trees. On some islands, the hillsides of small orange trees and the grey-green olive leaves give the landscape an almost Mediterranean feeling.

If you are based in Osaka, the easiest way into the park is often to the west, toward Kobe. The Rokko mountain range behind Kobe is part of Setonaikai National Park. From its ridges, you can look down over the port cities and across the water toward Awaji Island. On a clear evening, the lights of the whole Osaka Bay shoreline spread out below you in a long, glittering curve.

Further west, the park includes some of the best-known places in the region. The great floating torii gate of Itsukushima Shrine, on Miyajima near Hiroshima, stands in these same waters. Shodoshima, with its olive groves and deep autumn gorge, lies inside the park. So do many smaller islands that most foreign visitors never hear of, where the ferry might be the only way in or out.

In recent decades, the sea has found a new identity through art. Several islands now host contemporary art museums, outdoor sculptures and installations placed in old houses and fields. A large international art festival takes place across the islands every few years. It has brought new visitors to communities that were losing young people, and it has given the old fishing villages a second life.

Modern engineering has changed the sea as well. Huge suspension bridges now link Honshu and Shikoku across the water, including the long bridge over the Akashi Strait near Kobe. On a clear day, you can see their towers rising above the haze. Some travellers find them a contrast to the old harbours. Others enjoy them as part of the view — new steel lines drawn across a very old sea.

Whatever part of the park you reach, the best approach is slow. Take a ferry rather than a bridge if you can. Sit on the open deck. Watch the islands slide past and change colour as the light moves from silver to gold. Notice the small details: an oyster raft, a fishing boat with a red flag, a tiny shrine gate on a rocky point.

So take a moment now, wherever you are standing. Look out toward the water and count the layers of land you can see, near and far. Listen for engines, gulls, the soft knock of waves against a sea wall. This is a sea that people have travelled, fished and admired for a very long time. As you walk away, keep an eye on the horizon. The islands will still be there, fading quietly into the haze.