Sagrada Familia Cathedral
Legendary Catalan architect Antoni Gaudi dreamed of building a fantastic cathedral in downtown Barcelona, one with towers topped with sculptures of local fruit and a central nave that resembled a forest, capable of holding 14,000 worshipers. The Sagrada Familia began construction in 1883, but was only 15 percent completed when Gaudi was struck and killed by a streetcar in 1926.
The work on his masterpiece was subsequently disrupted by the Spanish Civil War, in which shelling destroyed the room containing his notes and designs. Eventually, in 1952, the project was restarted [sources: Gladstone]. But it's proceeded at a glacial pace ever since, due to its mind-numbing complexity and inconsistent funding. Unlike most of the behemoths in this article, this one is funded solely by donations and ticket sales. The cathedral has become a popular tourist attraction, generating $40 million (30 million euros) in ticket sales in 2011 [source: Tremlett].
That year, Joan Rigol, president of the building committee, announced that it might be completed by 2026, in time to honor the centenary of Gaudi's death -- or maybe two years later. At this point, nobody seems to even try to calculate the 560-foot (170-meter)-tall structure's total cost [source: Tremlett]. But at least this one isn't costing taxpayers anything.