Thousands of people flocked to Cramlington in the north east for the official unveiling by the Princess Royal. The Land Trust will manage the land mass with water shaped like a reclining woman, which sits within a 47ha country park.
No public funds were used to build a form over seven times the size of a football pitch with over four miles of paths that take 20 minutes to walk around. Northumberlandia water features cover the same area as ten Olympic-sized pools.
Blagdon Estate, on which the landform reclines, and mining firm the Banks Group invested around £3m in the project, which has taken two and a half years to build using stone, clay and soil extracted from the adjacent Shotton surface mine.
The trust will work with the Northumberland Wildlife Trust on sustainable ways to look after the landform, designed by Charles Jencks, as a visitor attraction. His sculpture took more than 10,000 hours to shape.
"Northumberlandia provides an iconic gateway feature to south east of Northumberland located close to the A1 and Newcastle Airport," said a trust spokeswoman.