If you have plenty of time to persevere with creating, importing and calibrating third party maps into Memory-Map you will find a rich source of really good maps on www.ign.es
which is the site for the Instituto Geografico Nacional. When you enter the site click on the small word "welcome" at the top right to get into the english language version of the site, then head for "Free download of digital geographic information for non-commercial use " within the Downloads section. You need to register to use this site.
To understand how to do this the best place to start is the help topic "Scan Maps" within the M-M application. But to really come to grips with this topic there are several very authoritative posts which specifically refer to the above source of spanish maps in various forum topics. So if you use the 'search' facility within the forum you will locate these discussions by searching for "spanish maps".
I have followed their advice and managed to create a lovely 1:50k map of the Picos de Europa to use with M-M.
Technically it's not for the faint hearted and among other things it involves using MAPC2MAPC to assemble and paste together all the map rectangles you have downloaded from the MTN25 series.
The web site for the Institut Cartografic de Catalunya (ICC) may also interest you if your exploration will be in Catalunya. It is http://www.icc.cat/
and you can zoom in and out through a large number of layers for different levels of detail. However I have not found a means of downloading rectangles of map in the way it can be done with the IGN(ES) site.