The Edward Stocks Massey Gallery was built in 1923 next to the Art Gallery on the second floor of the North wing to display watercolour paintings. It replaced rooms 47 and 49-51 as shown on the 1902 heating plan. According to the inventory of 1871, in the 19th century these rooms included the school room. Early in the 19th century, the room nearest the chapel had been Charles Townley's library.
From the 1970s, the room was often used for temporary exhibitions such as the Pendle Witches exhibition in 1972. When the Natural History Centre was closed in 2006, the Stocks Massey Gallery was divided into two in order to display natural history collections. These were displayed in eastern half with access from both the back staircase and art gallery. The western half was initially used as an education room for school visits but has now reurned to use as a display room, most often displaying watercolour paintings.
In 2015, the natural history collection was given a new home in the Wild about Burnley Room room and the eastern half was once more used for temporary exhibitions. It was named The Sanderson Gallery in 2017 in memory of Colin Sanderson who was for many years President of the Towneley Hall Society.