Complex sentence: Villanueva Sierra is proud to be the town where you held the first Arbor Day around the world, a initiative launched in 1805 by the priest of the place with the enthusiastic support of the entire population.
Split into simpler sentences: Villanueva Sierra is proud to be the town where was held the first Arbor Day around the world. A initiative launched in 1805 by the local priest with the enthusiastic support of the entire population.