The island of Madeira is wet in the north and west and dry in the south east. In the 16th century the Portugese started building lavadas [channels] to carry water south and east from the mountains to the agricultural regions. Madeira is very mountainous and building the lavadas was often very difficult. Many are cut into the sides of mountains.
There are also 25 miles of tunnels.
There are now over 1,350 miles of lavadas and they provide a magnificent network of walking paths through some of the finest scenery in the world. Some provide easy and relaxing walks through beautiful countryside. Others are narrow, crumbling ledges cut into the side of mountains where the slightest slip could result in serious injury or death. Two of the best are the Levada do Caldeiro Verde and the Caldeirao do Inferno. The two lavada are linked and are about 23 miles long in total. Both have a lot of tunnels and long sections which should not be attempted if you suffer at all from vertigo. Torches are essential for the tunnels. Helmets are also a good idea unless you are a midget.
On the Levada do Caldeiro Verde.
The best guide to the lavada and other walks on Madeira is "Landscapes of Madeira", published by Sunflower Books. This book won the Thomas Cook Best Travel Guide Award
This has detailed instructions on 42 lavada and mountain walks plus six road tours. The maps are superb and the book is well set out and easily carried. A good guidebook is essential because some of the levadas are hard to find. A few are signposted but many are not. I spent a couple of hours trying, unsuccessfully, to find one particular lavada. The authorities on Madeira need to recognise that the levadas are a real asset to their tourist trade and install proper signposting.