Complex sentence: The Old London Underground Company is a British startup company that has designed a business model to make value of London's Portfolio of Underground Space, using as its flagship, the change of 26 disused stations on the London Underground into tourist attractions.
Split into simpler sentences: The Old London Underground Company is a British startup company that owns the business model that makes value of London's Portfolio of Underground Space. The Legacy project details changes to 26 disused stations on the London Underground into tourist attractions.