The correct answer to this open question is the following.
You do not specify the country, the region, or the municipality you live in.
So what we can do is to write a sample of the letter so you can just add the names of your town and national heritage place.
So the following is an example.
Dear Sirs,
As a citizen of ______, I would like to firmly suggest that the Native American Indian archeological site known as ________ could be considered to be registered as a "world heritage site by the UNESCO."
As everybody knows this is a magnificent place where our ancestors lived and developed not only a city, but an entire culture comprised of history, traditions, rites, and customs. This culture has influenced the development of our towns and cities,
They not only built temples but roads and homes that allowed them to survive in the harsh winter season and could establish trade relations with other tribes of the region.
They created pieces of art that prove they were an artistic tribe too, and the paintings on the walls of the ceremonial centers it is valid proof of their talent.
Furthermore, of you the beautiful landscape of the land, I consider we have all the elements to ask UNESCO for registration as a "world heritage site."
Thank you very much for your help. And I'll wait for the good news.