This is an oversized open space in the center of Hanoi, just in the Ho Chi Minh Memorial Complex. It takes a security check to enter, but it is free. It will be super hot at noon in July. Note that the mausoleum area has a limit on opening hours. I think this is the square grass in front of Ho Chi Minh Mausoleum. The whole area is well maintained and there are many armed guards guarding it, but once you enter the site you can move around. They will hold a flag raising ceremony here but we didn't have time to watch it. There are many government buildings nearby.