Ireland's Historic Science Centre contains astronomical instruments, cameras, photographs and photographic equipment used by the Third and Fourth Earls and Mary, Countess of Rosse, in the middle and late 1800s. Also on display is electrical and engineering equipment originally belonging to Charles Parsons and used in his experiments as well as a large area devoted to the botanical work carried out in the Demesne. The whole collection is housed in the restored stables of the castle.
The grounds evolved from the parkland of oak and beech trees of the 17th century; of the same period are the Box Hedges which form part of the formal gardens. The 18th century is characterised by the creation of the lake and planting around this area.The 19th century saw the building of the Suspension Bridge and the development of the Fernery and the Fountain, the Waterfall and the Winter Garden. The 20th century saw the creation of the Arboretum, the River Garden, the terraces and herbaceous borders around the castle, the seed and plant expeditions abroad and the development of glass houses for propagation. Of the same period is the development of the formal gardens based on 17th century Bavarian design.The wildflower meadows are left uncut until July to ensure that the wild flowers seed and naturally regenerate.
Birr Castle itself is not open to the public.