Campo de Santana is a pleasant green space that, on September 7, 1822, was the scene of the proclamation of Brazil's independence from Portugal by Emperor Dom Pedro I of Portugal. The landscaped park, with swans and an artificial lake, is a fine place for a respite from the chaotic streets, and you're likely to see a few wild agoutis (hamster-like rodents native to Brazil) scuttling about.
Campo de Santana
Rio de Janeiro