Great Glasshouse (Tŷ Gwydr Mawr)

The Great Glasshouse stands almost on the site of Middleton Hall, the mansion that the architect Samuel Pepys Cockerell built for Sir William Paxton, who bought the estate in 1789 and laid out a water park of lakes, dams and cascades around it. Gutted by fire in 1931, the house was left a shell whose walls were pulled down some twenty years later; the estate, bought by Carmarthenshire County Council, was let to young farmers.

From 1978 local walkers took an interest in the park's remains and raised money that led to the rediscovery of several historic features. From that grew the idea of a national botanic garden for Wales, whose start-up costs were shared with the UK Millennium Fund. The glasshouse, entrusted to Foster and Partners with Nigel Curry as project architect, became its centrepiece. The garden opened to the public on 24 May 2000 and was officially opened by Charles, Prince of Wales, on 21 July; that year the practice won the Gold Medal for Architecture at the National Eisteddfod of Wales for the glasshouse.

In 2003 the garden ran into serious financial difficulties, and in 2004 it accepted a support package from the Welsh Assembly Government, Carmarthenshire County Council and the Millennium Commission. In 2009 the glasshouse stood in for the domed greenhouse in the Doctor Who episode The Waters of Mars. In 2025, the garden's 25th anniversary year, a £1.3 million grant from the Julia Rausing Trust launched the first phase of a multi-phase refurbishment.

Foster and Partners gave the glasshouse the form of a glass dome that the garden likens to a teardrop set in the landscape, covering the whole interior garden in a single span. When it was completed it was the largest single-span glasshouse in the world, a rank the garden still claims for it. It is 95 to 110 m long and 55 to 60 m wide, with a roof of 785 panes of glass, and the garden gives 3,500 m² of interior space.

Under this transparent shell, Kathryn Gustafson's landscape builds up rocky terraces, sandstone cliffs and gravelled scree slopes, creating a wide range of aspects and habitats. The garden was planned around recycling and conservation: recycled biomass supplies part of its heating, including for the visitor centre and the glasshouses.

Twenty-five years after opening, the refurbishment begun in 2025 addresses the mechanical plant, glazing and environmental control systems that keep conditions precise for the plants, with the aim of cutting energy use and meeting current sustainability standards. Inside, a hemispherical marble bench inspired by the building's form commemorates Nigel Curry, who died in 2024.

The glasshouse is devoted to the floras of the world's six Mediterranean-climate regions: California, Chile, South Africa, Australia (Western Australia), the Canary Islands and the Mediterranean Basin. Together these regions cover less than 2% of the Earth's surface yet hold more than 20% of all known flowering plant species, a diversity the garden ranks second only to tropical rainforest. It describes the glasshouse as home to the largest collection of Mediterranean plants in the Northern Hemisphere, and many of the species grown are endangered in the wild.

Each region has its own zone, with suitable soils and terrain. The garden singles out California lilacs and Western Australian flowers; in the Canaries section stand architectural dragon trees, alongside geraniums from Madeira and echiums whose spring flowering the garden compares to slow-motion fireworks. The glasshouse also serves as a living laboratory for conservation, research and education.

The glasshouse sits at the heart of the garden, which covers 568 acres (about 230 ha) in the Tywi valley in Carmarthenshire; the Med café is just inside its northern entrance. Allow at least an hour to take in the six zones. The garden recommends April and May, when the Mediterranean plants are at their blooming best.

The visit carries on into the Double Walled Garden, rebuilt from the ruins, the tropical glasshouse designed by the Welsh architect John Belle and opened in 2007, or the Waun Las national nature reserve, some 150 hectares of wildflower meadows and pasture reached from the garden. To the east, the restored view from the old mansion site runs out to Paxton's Tower, a neo-Gothic folly raised in honour of Lord Nelson.