Welwyn Garden City is a town in Hertfordshire, England, 20 miles north of London. It was the second garden city in England and one of the first …Welwyn Garden City is a town in Hertfordshire, England, 20 miles north of London. It was the second garden city in England and one of the first new towns. It is unique in being both a garden city and a new town and exemplifies the physical, social and cultural planning ideals of the periods in which it was built.