Why are houses so cheap in Spain?

Could you please explain to me the reason behind the surprisingly low prices of houses in Spain? I've heard rumors about the real estate market there being quite unfavorable, but I'd like to understand the actual factors that contribute to this situation. Is it due to a high supply and low demand? Or could it be related to the economic situation in the country? I'm quite interested in investing in Spanish property, but I want to make sure I understand all the nuances first. Thank you for your assistance.