A 120-acre demesne where 400 years of science meets breathtaking gardens — home to the world's largest telescope for 70 years, Ireland's tallest treehouse, and over 5,000 plant species, all in the heart of County Offaly.
Built in 1845 by the 3rd Earl of Rosse, this 72-foot-long reflecting telescope was the largest in the world for over 70 years. Through it, the spiral nature of galaxies was first observed. The fully restored instrument stands in the centre of the demesne — an awe-inspiring sight and Ireland's greatest scientific wonder.
Housed in the restored stable block, seven galleries cover astronomy, engineering, early photography, and the Parsons family legacy. Standouts include the Lunar Heat Machine, a letter from Neil Armstrong, Mary Rosse's pioneering photographic equipment, and the world's oldest intact darkroom (c.1840s), relocated and recreated here. A wheelchair lift connects both floors.
Explore four key garden zones: the Formal Gardens with the world's tallest box hedges and hornbeam cloister walk (planted 1936); the River Garden with 6th-century St Brendan's Well; the Castle Terraces for the best castle views; and the Fernery Garden with its 1880s waterfall, refurbished in 2024. The plant collection includes rare specimens from China, Chile, Mexico, and the Himalayas.
Newly enhanced with a spectacular tower and thrilling tube slide, the treehouse anchors a family-friendly playground with swings, slides, sand pits, and climbing frames. A dedicated space for young adventurers to burn off energy.
10 km of trails crisscross the demesne. Pick up maps at reception: the Red Tree Trail (5 km, 65 champion trees), the Engineering Trail (ages 12+), the Solar Trail (2 km scale model of the solar system), the Family Quest, the Flora Trail (May–June), the Gallery Challenge, and the Bird Spotters Guide. All included with general admission.
Birr Castle remains a private family home. Guided tours of the interior run Monday to Saturday from mid-May to early September. Tours cost €22 per person, must be pre-booked online, and are suitable only for ages 12 and above. Spaces are limited and sell out quickly in summer.
A 20-minute narrated train tour covering the Formal Gardens (exterior), the Great Telescope, and Birr Castle (exterior). Runs weekends April to August with departures at 12:30, 13:15, and 14:00. Costs €5 per person as an add-on to general admission. Pre-booking essential.
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