The centerpiece of the project is the 70-story Landmark Tower, Yokohama's tallest building; its observation deck affords a spectacular view of the city and the Bay Bridge, especially at night.
Due to construction regulations, Yokohama's tallest building is only 30 stories high. 
mnli hypothesis: Due to construction regulations, Yokohama's tallest building is only 30 stories high.  premise: The centerpiece of the project is the 70-story Landmark Tower, Yokohama's tallest building; its observation deck affords a spectacular view of the city and the Bay Bridge, especially at night.