Founded in 1626, the Paris Botanical Garden is currently a serious institution and leisure option. It's not too large, and plants are carefully tended to. It's divided into several sections, including a winter garden, tropical greenhouses and an alpine garden. It houses the Botany faculty. There is a zoo opposite. The most entertaining way to get here is with the Batobus ('http://www.batobus.com') which is boat that works as a bus along the Seine.