These ruins, rediscovered in 2011, reveal a fundamental part of Rio and Brazil history (and indeed that of humankind itself). On the unearthed stones, slavery left its mark; this site was South America’s largest slave port at which, between 1811 and 1831, it’s estimated that between a half-million to a million captured Africans were unloaded from ships and sold as slaves. Buried in 1843 to make way for a different wharf, this blot on history was hidden (at least for a time) but came to light once more as the neighborhood was being fixed up for the Olympics. It was named a World Heritage Site in 2017 and merits a visit, if only to recognize and atone for the tragedy it represents.