Serre de la Madone was created by Lawrence Johnston, the English-American garden designer better known for Hidcote Manor in Gloucestershire. Johnston bought the property in 1919 and spent two decades developing its terraces, walls, and water features, importing rare species from around the world.
Menton's microclimate allowed him to grow plants that could not survive a normal French winter, and the result is one of the most unusual private gardens in Europe. The Conservatoire du Littoral acquired and restored it in the early 2000s. Open by guided tour most of the year; book ahead. The walk up through the old town to reach it is worthwhile in itself.