Complex sentence: The site, lying close to a tributary of the Usumacinta River, was first seen by non-Mayans in 1946 by two American travelers who were shown the ruins by the local Lacandon Maya who still visited the site to pray in the ancient temples.
Split into simpler sentences: The site, lying close to a tributary of the Usumacinta River, was first seen by non-Mayans in 1946 by two American travelers. The Americans were led to the ruins by the local Lacandon Maya who still visited the site to pray in the ancient temples.