Ah, finding out the name of her neighborhood yielded better google results, and this article has proved illuminating.
It is apparently a five-bedroom, four-bedroom apartment bought for 1.8 million euros and extensively renovated. It is 468 square meters, or just over 5,000 square feet. Thus, though not a palace, is not at all cramped, especially as I presume Elena is there alone much of the time.
This also makes it a comfortable meeting place for her family, as we know Inaki Urdangarin has met his wife and children there while on his releases from prison, and I read that Juan Carlos took leave of family there before his departure. I should say part
of her family. Felipe and Letizia, I assume, are not