The construction of a rock garden in 1882 was prompted by a donation of 3,000 alpine plants. This represented one of the largest collections in the country at the time.
The garden emulates a Pyrenean mountain habitat, a 150-metre valley, with a winding path running through, simulating a natural watercourse. It was originally fashioned from limestone, this has been gradually replaced with Sussex sandstone, as it retains more moisture and allows a wider range of species to be cultivated.
The planting fits a geographic theme, with mountain plants from six major regions (Europe, Africa and the Mediterranean, Asia, New Zealand and Australia, North America, and South America) represented.