To develop the basement the builder has gave the following as a rough estimate -
1. to develop the entire basement level and prepare one cinema room and one gymnasium- €100,000 (this does not include the machinery which he says will be around 20k on top of this figure)
2. He also suggested that you may wish to relocate the existing machinery room under the new pool hence increasing the lower level even further.
You should also keep in mind that the above ground level build figures for La Zagaleta is 15% of the plot which means that there is even scope to extend here should you so wish in the future, again adding significant value to the villa. Currently excluding the basement the villa is 493.88 sq m and an additional 200 sq m would be permitted from ground level upwards. Superb opportunity you may wish to explore in the future which really would take this property to an even greater level.