What to see

So what's visible at a dark site in Spain?

There are two parts to the answer. The first is that since the sky here is much darker than in an urban environment, you can see a great deal more detail. The other part is that as the location is closer to the equator than places in northern europe, or the northern USA, you can see features that never rise above the horizon. This also means you get more seasonal variation than at locations further north.

Look at the two maps of the sky below. The one on the left is how the sky looks from London. On the right is a map of the sky from Cuevas del Negro. You'll see that the CdN map appears to be shifted upwards compared to the London map.
In each map I have marked the position of the Pole Star with a pink dot. The difference in position of the pole corresponds to the 14° difference in latitude between the two places. As you can see, for the time the maps were produced the constellation Centaurusis visible from CdN, but from London it is below the horizon.
This does mean that some constellations above the Pole Star on the map are below the horizon at CdN. However if you wish to see them, they will rise later in the night - or could be viewed at a different time of year.