I'm in a similar situation (also in Spain). We have a ruined house that we eventually want to demolish and rebuild, and we have a lot of rubble from redoing our roof (mostly mud, cane and crumbled roof tiles). We are thinking of using the rubble to build "stairs" to go up and down terraces.
Also, recently we thought of converting one of our crumbling water deposits into a natural swimming pool, and we could use a lot of material to fill in.
Another option is to use it to fix access roads, we have a local guy with an excavator and he does wonders with a pile of rocks
In my experience in Spain, especially with old, rural houses (I don't know if it's your case, but it's definitely mine) it's common to find broken pieces of asbestos/uralita, so keep an eye out for that.