Complex sentence: The building was used to hold a dinner hosted by Charles, Prince of Wales to celebrate the 80th birthday of Queen Elizabeth II on 21 April 2006-a few days later it reopened as a visitor attraction.
Split into simpler sentences: The building was used to hold a dinner hosted by Charles, Prince of Wales to celebrate the 80th birthday of Queen Elizabeth II on 21 April 2006. A few days later it reopened as a visitor attraction.