Palm House (Butterfly House), Williamson Park

Williamson Park occupies former moorland above Lancaster, pitted with the quarries that supplied the stone for most of the city's buildings. From the 1870s James Williamson senior had the ground laid out by the designer J. Maclean; his son, James Williamson, later Lord Ashton, continued the work and handed the park to Lancaster Corporation in 1881 with an endowment of £10,000.

A new round of improvements, which Lord Ashton offered to pay for, began in 1904. Its centrepiece was the Ashton Memorial, built in 1907-09 to designs by Sir John Belcher as a memorial to Lord Ashton's second wife. The palm house, designed around 1909 by Belcher and Joass, was placed about 40 metres east of the memorial, facing its entrance.

The glasshouse was damaged by fire in 1949. It was restored around 1985 and now houses a butterfly house. The building has been listed Grade II since 18 February 1970, and the park is on the Register of Historic Parks and Gardens of England as Ashton Memorial Gardens and Williamson Park.

The glasshouse has a rectangular plan under a convex hipped glass roof. It is built of brick on a sandstone plinth, with timber and metal glazing bars, while the columns and entablature combine timber and painted render.

The symmetrical west front is framed by rusticated brick end piers. At its centre opens a semicircular porch of six Tuscan columns, flanked on each side by three bays divided by similar columns and filled with windows with glazing bars. Above runs a Doric entablature topped by an urn over each column. The attic has a circular glazed opening in each bay, between pilasters, and a Diocletian window at the centre.

On the axis, the front wall opens through three tall glazed openings; the wider central one holds the double doors, which project forward under a segmental pediment. About 40 metres to the west rises the Ashton Memorial, a Baroque building in Portland stone some 50 metres high, designed by Sir John Belcher.

Since its restoration, the former palm house has been home to a tropical butterfly house, where exotic butterflies share the space with birds. The species highlighted in descriptions of the site include the blue morpho, the emerald swallowtail and owl butterflies, whose camouflage deceives the eye.

The building is complemented by a small zoo: a mini-beasts area, a bird enclosure and a small-mammal section, home among others to meerkats and marmosets. Described as newly renovated by Visit Lancashire, the butterfly house welcomes many guided school visits, and meet-the-keeper sessions are offered to the public.

The butterfly house stands at the top of Williamson Park, on the hill overlooking Lancaster, about 40 metres from the Ashton Memorial. A visit naturally combines with the memorial, which houses the Williamson Gallery and offers views as far as the Fylde coast and the Lake District. Laid out in former quarries, the park has woodland walks, play areas, a café and a shop, and through the year it hosts concerts, exhibitions, guided walks and the Dukes Theatre's open-air performances.