A bridge to mainland China
China is apparently planning to build a bridge from mainland China to Taiwan proper, a distance of 180km across water.
I can think of many groups of people with potential members that would want to damage such a bridge, if it were ever completed.
Also, given the Hong Kong – Zhuhai – Macau bridge will be 29km and cost around 6 billion USD, I have to wonder how much this cross strait bridge would cost. It would cross a deeper seabed and would be even more exposed to things like typhoons. It would also have to deal with major earthquakes.