It is a church. A beautiful one but it is still in use so be respectful. It is within walking distance from the War Remnant Museum. In fact, you will pass the main gate of The Independence Palace to reach Saigon Notre-Dame Basilica.
There are plenty of cafes nearby so you can enjoy a drink while appreciating the architecture of the building.
I didn't spend long here as the weather was gloomy and I wanted to get to Ho Chi Minh City Museum before it starts to pour!