Complex sentence: The Hypogeum of Ħal-Saflieni is a very popular tourist attraction, because of its age, Heritage Malta (the government body that looks after historical sights) only allows 80 persons per day to visit the Hypogeum.
Split into simpler sentences: The Hypogeum of Ħal-Saflieni is a very popular tourist attraction. However, because of its age, Heritage Malta (the government body that looks after historical sights) only allows 80 persons per day to visit the Hypogeum.