The Life Mounds are the first thing you see as you drive through the gates of Jupiter Artland, a sculpture park in the grounds of Bonnington House, outside Edinburgh. Newly completed, these eight man-made hills have been shaped by the distinguished US critic, polemicist and designer Charles Jencks. Beautiful things, they rise in stepped ramps sheathed in emerald green turf, clustered around swirling ponds.  Last week, I climbed and sat on top of the tallest of these escarpments, as swallows performed aerobatics over the insect-rich waters. The Life Mounds called to mind the landscapes of ancient standing stones and barrows, of south-east Asian rice terraces, of patterns seen through a microscope; there was something of the spiralling forms of far-flung galaxies. All of these things (perhaps not the rice terraces) are acknowledged influences. Over the decades – he is a notably young 70 – Jencks has written a number of spirited books on modern architecture. It was his Modern Movements in Architecture, published in 1973, which helped me see that what had passed for a monolithic, single-minded Modern Movement had been no such thing. It was Jencks who identified the shift away from the certainties of modernism into the vagaries and rich (and sometimes indigestible) experiences of postmodernism: The Language of Postmodern Architecture, written 30 years ago by Jencks, remains a bestseller. And it is Jencks who, I can't help feeling, has begun to tire of the intellectual thinness of much contemporary "iconic" architecture, and to look for something beyond its ephemeral nature.  "Have I turned away from architecture? No, it's not that," he says when we meet at Portrack House, his home near Dumfries. "But I do believe architecture, and all art, should be content-driven. It should have something to say beyond the sensational. But, yes, the lack of culture in so much new architecture is worrying." Jencks wants to shape works that make us stop and think about our place, not just in the here and now, but in the cosmos. "It's something people have done even before they built Stonehenge, so why not now?"  The biggest woman in the world  Over the past decade and beyond, Jencks has fused a hungry interest in cosmology with his love and encyclopaedic knowledge of architecture and landscape art. This vision is explained in a new and engaging book, The Universe in the Landscape. "Not everyone will get it," he writes, with touching honesty. The Life Mounds at Bonnington are informed by cosmic patterns, as well as the molecular structure of cells at the point where, for good or carcinogenic ill, they divide. This stunning landform turns out to be a meditation on life and death.  "I've been a lucky man," Jencks says. "I've only faced one real tragedy: the death of my wife, Maggie, from cancer in 1995." Maggie Jencks was an innovative garden designer; together, throughout the 80s and 90s, the couple created their Garden of Cosmic Speculation in the grounds of Portrack House. Maggie's Centres, a number of cancer care clinics designed by world-famous architects (Frank Gehry, Zaha Hadid, Richard Rogers) were her idea, and is a scheme that has continued in her honour.  Jencks is now working on an enormous project just north of Newcastle. He has been commissioned by a UK coal-mining company to create a land form that will soften and enhance an otherwise challenging landscape. "Northumberlandia" (the name is his, intended to suggest a land goddess) is currently under construction, and due for completion in 2013. A giant effigy, in clay and soil, of a recumbent naked woman rising 34 metres (her breasts) and measuring 400 metres from head to toe, she will, Jencks says, be "the world's largest human form sculpted into the landscape".  Such figurative interpretations of earth goddesses could be seen as kitsch. But Jencks argues that she will fold, if not quite blur, into the landscape. Still, compared with the layers of cosmological meaning embedded into Portrack and Bonnington, this is clearly a populist work, one its patrons hope will become a major tourist attraction.  The Gretna Landmark Project should be one, too. Details have yet to be unveiled, but this ambitious work will mark one of the key border crossings between Scotland and England. Developed by Jencks and the artist Andy Goldsworthy, the final design will also involve the disparate talents of designer and engineer Cecil Balmond, California artist Ned Kahn and British architect Chris Wilkinson. Expect the unexpected, and certainly the bold and eye-catching.  Meanwhile, Jencks and his 30-year-old daughter, Lily, an architect and landscape designer, have been working on a design for CERN (the European Organisation for Nuclear Research) near Geneva. Their brief is to give this hidden wonder of the modern world (its workings are mostly underground) a physical presence. "There is no question," says Jencks, "that this Vatican of Science, with the visage of Heathrow Airport, desperately needs urban definition." As far as I can make out, the end result will be a pair of giant interlocking question marks made of grassed earth closing around, and interrogating The Globe – a hollow timber sphere originally designed for the 2002 Swiss Expo by architect Hervé Dessimoz.  In Jencks's view, cosmic passion, or the desire to know and relate to the universe, is one of the strongest drives in sentient creatures. The power of neolithic henges and bronze-age barrows, of the Uffington White Horse and some of the greatest buildings of all time – the spiral minaret at Samarra in Iraq, the Pantheon in Rome – lies in their elemental qualities. Their meanings are not explicit, yet they send shivers of recognition down the spine. The Life Mounds at Bonnington, to my mind Jencks's best landform work to date, have that effect on me.
His swirling 'land sculptures' are inspired by molecular biology and outer space. Architect Charles Jencks tells Jonathan Glancey about his most ambitious project yet