A collapsible enclosure comprising a plurality of support arms, supporting a canopy and movable on a track, from a stored position in which the support arms lie side by side in a substantially horizontal configuration, to an in-use position in which the support arms are erected in spaced apart arrangement in a substantially vertical configuration to define an enclosure, and means to hold the support arms in the spaced apart condition. Preferably the support arms are stored in an underground structure at the location where the enclosure is to be erected.