For the last 40 years Richard Long has been walking in the name of art. It began in Somerset in 1967 when, while still a student at St Martin's, he took a stroll on a beach and rearranged the stones to invoke his presence within the landscape. Since then his walking has taken him around the world, from the Himalayas to South America and Africa, and all the time he has been recording the evidence of his journeyings, and using rocks, wood, mud and water from the locations to create some of the most original, beautiful and resonant works ever seen in British art.

There is a curious sense of homecoming about this, Long's first UK retrospective for 16 years. For one thing, unsurprisingly, the diverse and inspiring landscape of Scotland has often featured in his work. For another, it was here in Edinburgh in 1974 that he had his first major show.

What we see in the gallery is an impression of the landscape in the most visceral sense: a pure and poignant memory conjured up through a combination of photography, maps, written text and found objects to create installations which are at once exquisite, hugely engaging and deeply emotive.

Although not strictly chronological, this superbly hung show, installed with care by the artist himself, does paint a lucid picture of the development of Long's work. His art is arduous in the extreme and he pushes himself to physical limits which many artists would decline. It is worth remembering, when looking at the sublime beauty of this show, that most of it was made only through pain and loneliness.

The major focus of this show falls on four new wall paintings and a single floor piece. Stone Line, made in 1980 and now, thankfully, in the collection of the National Galleries, occupies the whole of Room 8. The first cut slate work Long ever made, it consists of dozens of carefully selected, unchanged pieces of slate, set together so they appear to be contained within a perfect rectangle. The result is spectacular. The stones, crisply defined against the floor, with a discreet sheen on top and strong shadow underneath, encapsulate a collision of man and nature.

Principally, Long is a poet, not least in his texts, which hang here, punctuating the paintings, maps, photographs and objects, as haiku-like suggestions through which we navigate to replicate the artist's experience. A prime example is the wall of the final room, on which Long has hung two photographs of a work on Dartmoor along with a text - 'Speed of the Sound of Loneliness' - which imparts, through rhythm, time and verbal association, as close a sense as he ever gets of taking part in the real thing.

Mud has played a major part in his work since the late 1970s. He is acutely aware of its implicit nature as a material produced by the flow of water over the earth. While in one work he throws liquid mud from the Forth, Pollock-like, at a wall, in a larger piece he contains it within a semi-circle, perfectly in tune with the room's architectural detail, yet within this constraint allows the material to work for itself. This is central to Long's philosophy - that while the artist can choose and direct the materials, it is the materials themselves, governed by nature, in this case gravity, which actually create the work.

One of the most sublime moments in this show is getting up close to the second huge wall painting, made using liquid chalk from the Cairngorms. It is possible to follow the imprint of the artist's fingers as they snake intuitively across the wall, calling to mind the hand of Titian as in his finest, final works, he applies paint directly to the canvas.

Heart-stopping as this is, it's still not quite the ultimate experience on offer. Look out of the window and you will see an example of the artist's most direct intervention with the land. In the garden of the gallery Long has created a slate cross, embodying the concept of danger and beauty and effectively uniting the exhibition with the external environment, and so breaking down conventional boundaries.

If you do anything this summer, visit this show. At a time when we are constantly warned of the erosion of the very fabric of our world, this is a poetic clarion call for us to acknowledge our place in the environment and our individual responsibility. For if we do not, then all that we will have will be a memory.

- Iain Gale