Final answer:
Nebuchadnezzar is best known for his extensive rebuilding of Babylon, including its famous walls and gates, and the possibly legendary Hanging Gardens. He also constructed the Ishtar Gate and contributed to the development of ziggurats like Etemenanki.
Step-by-step explanation:
Nebuchadnezzar's most significant building achievement was the extensive rebuilding of Babylon, including its fortification walls, palaces, and seven gates. Additionally, he is associated with the creation of the Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World, although its existence may be more legendary than historical. His works not only showcased the grandeur of Babylon but also demonstrated the advanced architectural capabilities of the Neo-Babylonian period.
Apart from the legendary gardens, Nebuchadnezzar's building endeavors also encompassed the renowned Ishtar Gate, which was part of an elaborate fortification system made from blue glazed tiles adorned with representations of dragons and bulls. Moreover, the construction of the immense Babylonian ziggurat, Etemenanki, was another testament to his architectural vision, though the structure did not survive to the present day.