5 Dollars Florence Cathedral

Palau's tourist-dollar silver program, running since the late 1990s, has issued dozens of architectural and natural-wonder themes under licensing arrangements that generate revenue without any expectation of domestic circulation. Florence Cathedral — the Cattedrale di Santa Maria del Fiore — took 140 years to build, with Brunelleschi's dome not completed until 1436, solving an engineering problem that had stumped builders for decades after the drum was already standing.