The parks in Lisbon are among the city's most pleasant and attractive public green spaces. The most famous however is found outside the Portuguese capital, at Sintra. The beautiful and historic Parque do Palácio Pena is in fact part of a UNESCO World Heritage Site and embraces several majestic monuments and an ancient castle. Nearer Lisbon but still out of the city is the wonderfully original Parque dos Poetas, a park themed around Portuguese and Portuguese-speaking poets and writers. Dominating the city outskirts is Parque Florestal de Monsanto, a huge wooded area known as "Lisbon's lung" criss-crossed with walking trails and known for its biodiversity. Central Lisbon's biggest green space is Parque Eduardo VII, which sits at the top of Avenida da Liberdade and dates from the early 20th century.Within the park are the famous estufas, greenhouses brimming with exotic tropical flora. Visiting the Belém Palace Gardens is a rare opportunity to explore the grounds of the presidential palace while the nearby Jardim Botânical Tropical affords encounters with flora originating from the Far East. At the top of Belém sits another tropical garden park, Jardim Botânico da Ajuda.Back in the city centre, two parks stand out, the Parque Príncipe Real, noted for its huge cedar tree, and Jardim da Estrela, arguably the prettiest and most tranquil of all Lisbon's parks.