Chelsea Physic Garden.  London, UK.

 

"The Chelsea Physic Garden was founded in 1673, as the Apothecariesā€™ Garden, with the purpose of training apprentices in identifying plants. The location was chosen as the proximity to the river created a warmer microclimate allowing the survival of many non-native plants ā€“ such as the largest outdoor fruiting olive tree in Britain ā€“ and more importantly, to allow plants to survive harsh British winters."  Source: Garden website.