Both Painshill Park Trust and their contractor Cliveden Conservation were recognised by RICS for the exemplary restoration of the folly, created by the Honourable Charles Hamilton between 1738 and 1773.
Funding for this heritage project included private donations and a grant from the Heritage Lottery Fund (HLF).
The awards judges said the restoration had been a complex and lengthy process of "painstaking" analysis of historic records, paintings and drawings to recreate the grotto.
Recreation of this important historic folly combined extensive research of archive material and archaeological data, with landscaping and expert craftsmanship. Hundreds of thousands of crystals – calcite, gypsum, quartz and fluorite – including originals recovered from archaeological works, were skilfully embedded with lime mortar onto a framework of inverted wooden cones, to re-create the dazzling stalactite effect of the original folly. Historically, this folly was known as being the finest stalactite grotto in Europe.
Michael Gove, chief executive of Painshill Park Trust Ltd, said: "We are thrilled to win this award as the re-creation of the grotto is a tremendous achievement. It was a pleasure to work alongside the skilled team from Cliveden Conservation and we are extremely grateful to everyone who was involved in the project."
The crystal grotto along with the other category winners will be entered into the RICS Awards 2015 Grand Final on 16 October.