It was the last hill taken by the Viet Minh, marking the end of the battle, and was the scene of some of the most intense fighting, and loss of life.
The hill was eventually blown up from underneath by the Vietnamese, so what's on display here is mostly a reconstruction, making it, by our reckoning, the world's largest, open-air, diorama in situ.
Nevertheless, it does provide a vivid and striking picture of what the Viet Minh took on, in terms of military logistics, and if you can imagine the challenge of taking on such a well-entrenched hill from the ground, and then multiply that by six, you'll understand why the Vietnamese are deservedly proud of the victory, and why it had world-wide repercussions.
The maze of trenches is extensive and elaborate, and would have provided cover for hundreds of troops to fire from a protected position on high ground at any force attacking from any direction. The French certainly didn't lose for lack of trying, and that's what A1 Hill is on display to demonstrate. They lost due to a fatal miscalculation. They were unaware that long before they broke ground on the garrison at Dien Bien Phu, the Viet Minh had already anticipated the move, and had begun the long arduous process of moving heavy artillery into secret positions encircling the location.
After you enter the front gate, take the road up the hill to the right. Once you're at the top you'll find some bunkers that can be explored, giving access to the trenches. This commemorates the period during the conflict when the Viet Minh took the hill, but then were pushed back, before finally routing the French troops for the last time.
The nearby cemetery will have deep meaning for those connected to the conflict on the Vietnamese side, but for the casual tourist it's just another Vietnamese cemetery and you might want to skip it.