Complex sentence: This was once a run-down area, housing little more than a ventilation-fan building for the Central Artery Tunnel; however, a garden was constructed at this site as part of the Big Dig project.
Split into simpler sentences: This was once a run-down area, housing little more than a ventilation-fan building for the Central Artery Tunnel. However, a garden was constructed at this site as part of the Big Dig project.