Kew Gardens in southwest London is a worthwhile hotspot for tourists and garden enthusiasts alike. Its 300 acres are home to more than 30,000 species, a herbarium collection estimated at 7 million preserved plants, and a library with 750,000 volumes. Standouts include the five 250-year-old trees dubbed "Old Lions,"a treetop walkway, and several glasshouses recognized for their architecture as well as the plants inside. The crescent-shaped Davies Alpine House looks straight out of a sci-fi movie and in the spring months displays exotic bulbs, including the striking Chilean blue crocus (Tecophilaea cyanocrocus).
Renowned for its research and conservation efforts, Kew is home to Botanic Gardens Conservation International, the largest network of gardens; and at Wakehurst Place in Sussex they run the Millennium Seed Bank whose goal is to conserve one fourth of the world’s plant species from wild sources by 2020. Garden enthusiasts should consider side trips to Kew's sister gardens and temperate woods at Wakehurst Place and the Royal Horticultural Society's Garden Wisley. [kew.org]