I downloaded the official shapefiles for the municipalities of Spain from INE here.
It has a lot of shapefiles, but I found out that the right one for what I need is esp_muni_0109.shp. I would like to convert these shapefiles to WGS84 with ogr2ogr. The problem is that these shapefiles have no .PRJ files, so I don't know from what projection system to convert them from.
Does anyone know the right projection system for these shapefiles and, if so, can anyone tell me what parameters to use with ogr2ogr?