This is an 18th century hermitage that survives in Manor Gardens. Back in the 18th century wealthy estate owners were hiring real people to dress as druids, grow their hair long, and not wash for years. These hired hermits would lodge in shacks, caves, and other hermitages constructed in a rustic manner in rambling gardens. It was a practice mostly found in England, although it made it up to Scotland and over to Ireland as well.
The ornamental hermit vanished at the end of the 18th century. In The Hermit in the Garden, Campbell chronicles the remains in a "catalogue of hermitages," listing whether they are destroyed, extant, or never built at all. However, the humble hermit may not have left us entirely. As Campbell argues, "the garden hermit evolved from the antiquarian druid and eventually declined into the garden gnome."
Source: Gordon Campbell, 2013, The Hermit in the Garden: From Imperial Rome to Ornamental Gnome