The combination of population growth, advancement in technology, and bigger governments has produced the need and ability to construct ridiculously expensive infrastructure objects that cost tens of billions of dollars.
The purposes of these projects vary; they range from the practical and the ostentatious. Whatever the reason though, it is a testament to the ability of modern institutions to concentrate massive amounts of wealth and mobilize a gigantic amount of labor and materials. They're also evidence of the wealth of the countries that constructed them.
The following is a list of 5 recently-constructed structures around the world that fit the criteria from the description above.