If you want to understand a bit of how Salvadoran society and culture developed, from precolonial times to the present day, this is the place.
A good overview of El Salvador's peoples and cultures.
To get a grounding and background of Salvadoran culture and society since pre-Columbian times, head to the southern end of the Avenida de la Revolución, where you'll find the city's oldest (1883) and perhaps still most popular museum. Its five halls are full of interesting displays including original objects both artistic and mundane, from all eras of history, and you can dip in for a quick overview or spend hours perusing the exhibits more in depth. You can also take advantage of being in the neighbourhood to pop over to the nearby MARTE museum of art or stroll up the Alameda Manuel Enrique Araujo to the iconic Divine Saviour of the World monument.