There is a possibility that you have to file this declaration.
720 is an INFORMATIVE declaration. That means that it is only about giving information to the Tax Office, not about paying a tax.
What you have to report is: assets outside Spain that exceed certain figures: for example, properties (houses, apartments), money in current accounts, shares, insurance policies, etc. that exceed 50.000€.
Therefore, if you have a property outside of Spain, and it is valued at over 50.000€, you must file the 720 declaration.
Here is a link with FAQS about this tax.

“720 is an INFORMATIVE declaration. That means that it is only about giving information to the Tax Office, not about paying a tax. “
PLEASE NOTE: The fines for not filing this declaration are ASTRONOMICAL…….SO IT IS OF ABSOLUTE IMPORTANCE TO KNOW IF YOU HAVE THE OBLIGATION TO FILE IT OR NOT. (I am sorry if I have just scared you, but it is true!)
If you have any questions, just contact us and we will give you the peace of mind you need.
On this subject I encourage you to read our post:
AM I A RESIDENT, A FISCAL RESIDENT OR SIMPLY NOT A RESIDENT OF EITHER KIND?
In which I give you the most important tips.
You should also read our post:
HOW TO PROVE THAT YOUR ARE A TAX RESIDENT OR A NON TAX RESIDENT

As is normal, being a RESIDENT in a country that is not yours, implies a concern for all those new things that are unknown to us, especially on the subject of TAXES.
Therefore, count on us to resolve any questions you may have or for any situation that makes you anxious.
Remember our MISSION STATEMENT: WE GUARANTEE YOU PEACE OF MIND & THESE AREN’T JUST WORDS
PS. Do you have the peace of mind that your Will is correct?. PLEASE CHECK MY WIL.