Wellington's scenic natural harbour and green hillsides adorned with tiered suburbs of colonial villas are popular with tourists. The central business district (CBD) is close to Lambton Harbour, an arm of Wellington Harbour, which lies along an active geological fault, clearly evident on its straight western shore. The land to the west of this rises abruptly, meaning that many suburbs sit high above the centre of the city. There is a network of bush walks and reserves maintained by the Wellington City Council and local volunteers. These include Otari-Wilton's Bush, dedicated to the protection and propagation of native plants. The Wellington region has  of regional parks and forests. In the east is the Miramar Peninsula, connected to the rest of the city by a low-lying isthmus at Rongotai, the site of Wellington International Airport. Industry has developed mainly in the Hutt Valley, where there are food-processing plants, engineering industries, vehicle assembly and oil refineries.