The garden is dominated by the ruins of Kildrummy Castle, listed category A. Originally built in the 13th century, it was repaired and extended during the 16th century. Burnt in 1690, it was partly repaired and then finally dismantled in 1715. The crumbling walls were extensively repaired from 1898. In 1952 the ruin was given by the Yates family into the guardianship of the state under the care of the Historic Buildings and Monuments Directorate.
Kildrummy Castle Hotel, formerly Kildrummy New Castle, is listed category B and is leased from the estate. It was built by A. Marshall Mackenzie in 1900 for Colonel Ogston. To the south there are extensive terraces set on top of the hillside with fine balustrades capping tall retaining walls. The New Castle and its terraces are English neo-Jacobean in style. Kildrummy Bridge is a fine single-span bridge across the gorge; it was built at the same time as the New Castle by A. Marshall MacKenzie and is a replica of the Brig O' Balgownie. The Lodge too was built c.1900, following the construction of the new drive. Castle Cottage is now occupied by the Head Gardener. Several interesting stones have been sited throughout the garden. Stone Benches, with sculptured lion supports from Warter Priory, Yorkshire, are thought to date from the 18th century.
The shelterbelts surrounding the garden are mainly of beech although some were replanted c.1900 with mainly conifers. To the north of the hotel the shelterbelt was planted with deciduous trees during the 1960s. The north side of the avenue to the Hotel is lined with beech. The west shelterbelt is a mix of soft and hardwood specimens.
In 1904 the flowing burn of the Back Den was dammed and turned into several large pools connected by a series of intricate cascades. The magnificent rock work was constructed by a Japanese firm of landscape architects. The Yorkshire firm of Backhouse under the direction of Mr David Peary transformed the old quarry. The banks are spanned by the imposing single-arched bridge. The steep sloping sides are planted with a range of unusual trees and shrubs, many of the more tender varieties growing in the warm shelter provided by the quarry face. Alpines are grown in the quarry.
The paths zig-zag down the escarpment, leading the visitor through the fine collection of plants. Along the valley floor and around the water's edge, bog plants are carefully placed. The most notable bog plants are Lysichitum americanum and Ranunculus lyalli from New Zealand. Under the face of the quarry is a rock garden in which gentians and other interesting plants are well established. Several small stones decorate the garden and a small summerhouse has recently been turned into a museum.
The guidebook lists over sixteen pages of plants and particularly notable are Quercus robur 'Purpurescens', Embothrium lanceolatum, Rhododendron varieties including 'Hummingbird', 'Fabia' and many others. Euonymus europaeus 'Hamiltonianus' and a particularly fine Schizophragma hydrangeoides grow up the cliff face. Throughout the slopes there are further collections of Primulas, Meconopsis, Gentians, Violas and other acid-loving plants. Many of the plants have been grown from seed collected throughout the world especially in New Zealand. At the western end of the ravine, Alan Mitchell of the Forestry Commission has measured over 24 tree specimens including a large larch (Larix decidua) (121'), a multi-stemmed Sciadopitys verticillata (the Japanese Umbrella Pine), a large cut-leaf beech, and a yellow elm (Ulmus glabra 'Lutescens'). During the last 25 years the Smiths have added an interesting collection of trees and shrubs, including specimens of Wellingtonia (Sequoiadendron giganteum), Cryptomeria japonica, Sequoia semprevirens and Metasequoia glyptosroboides.
Two large terraces surround the hotel on the south and west sides established following the construction of the house c.1900. Large rhododendrons, planted around this time, swamp the balustraded walls and mask views to the Castle. An enormous Hydrangea petiolaris grows up the walls of the building but otherwise there are few interesting plants and the terraces are grassed. In the north-west corner there is a sundial surrounded by stone seats.
The kitchen garden lies on a south-facing slope just below the large terraces of the New Castle. Enclosed by beech hedges it was made at the same time as the house was built. Today it is run as a small nursery supplying plants for sale at the garden. There are also two small greenhouses; one is heated. Part of the garden is lying fallow whilst the remainder is used for growing vegetables.