Complex sentence: Built upon a huge mound, and visible from most parts of the town, the origins of the mound are unclear, but it has been suggested that it may have been a passage grave similar to Newgrange.
Split into simpler sentences: Built upon a huge mound, it is visible from most parts of the town. The origins of the mound are unclear, but it has been suggested that it may have been a passage grave similar to Newgrange.