When I first encountered this tree on my trip to Barcelona in April '07, I thought it was a baobab (Adansonia), though the climate was all wrong for it, and the specimens below hardly seemed likely to reach the massive size typical to that African tree. Also, baobabs don't typically have the thorns (technically "emergences") that this tree exhibits.
The tree isn't baobab - it's Ceiba speciosa, or silk floss tree, but they both belong to the same family, Bombaceae (kapok - another species of Ceiba - is also in this family). Ceiba is native to South America and typically has the bottle-shaped trunk you see above, as well as distinctive thorns. It can also tend to lean, thus meriting the common Spanish name of palo borracho, which means 'drunken tree.'
As forbidding as this tree looks when it's defoliated, they are quite striking when covered in pink blossoms.