Spiritualism is the belief that the spirits of the dead have both the ability and the inclination to communicate with the living.
 The afterlife, or the "spirit world", is seen by spiritualists, not as a static place, but as one in which spirits continue to evolve.
 These two beliefs: that contact with spirits is possible, and that spirits are more advanced than humans, lead spiritualists to a third belief, that spirits are capable of providing useful knowledge about moral and ethical issues, as well as about the nature of God.
 Some spiritualists will speak of a concept which they refer to as "spirit guides"—specific spirits, often contacted, who are relied upon for spiritual guidance.
 Spiritism, a branch of spiritualism developed by Allan Kardec and today practiced mostly in Continental Europe and Latin America, especially in Brazil, emphasizes reincarnation.
Björn Emil Oscar Nyberg (11 September 1929 – 16 November 2004), was a Swedish fantasy author best known for his additions to the series of Conan stories begun by Robert E. Howard.
 His primary contribution to the series was "The Return of Conan" (1957), which was revised for publication by L. Sprague de Camp.
 He lived in France.
Sargent's Pond is a man-made 3 acre pond on Sargent Road in Brookline, Massachusetts.
 The pond was created by Charles Sprague Sargent (best known as the first director of the Arnold Arboretum) in the late 1870s as a centerpiece of his family's extensive Holm Lea estate.
 Sargent's estate has since been subdivided, but the roads giving access to it run along the estate's original alignments, and are private roads.
 Sargent landscaped the estate using similar principles to those he applied at the Arboretum, with vistas and a variety of trees and shrubs.
 The pond was created by damming a brook.
 It still has naturalistic plantings around it, although some Sargent's rhododendrons (a significant draw on occasions when he opened the estate to the public) have died.
Isaac Sprague (September 5, 1811 – 1895) was a self-taught landscape, botanical, and ornithological painter.
 He was America's best known botanical illustrator of his day.
Erik Sprague (born June 12, 1972), better known as The Lizardman, is an American freak show and sideshow performer, best known for his body modification, including his sharpened teeth, full-body tattoo of green scales, bifurcated tongue, subdermal implants and recently, green-inked lips.
 Rumors that he hoped to get a tail transplant have been debunked by Erik himself, who states that it would be impossible.
Charles Sprague Smith (1853-1910) was a Columbia University professor, best known for being the founder and director of the People's Institute.
Murray Fletcher Pratt (25 April 1897 – 10 June 1956) was an American writer of science fiction, fantasy and history.
 He is best known for his works on naval history and on the American Civil War and for fiction written with L. Sprague de Camp.
Kenneth Ray Sprague (born July 14, 1945) is an American bodybuilder, businessman, author and school teacher.
 He is best known as the owner of the original Gold's Gym in Venice, Los Angeles, which he owned and managed between the years 1972 and 1979.
The Sonate pour flûte et piano (Flute Sonata), FP 164, by Francis Poulenc, for flute and piano, was written in 1957.
 It is dedicated to the memory of Elizabeth Sprague Coolidge, an American patron of chamber music.
 Poulenc composed it for the flautist Jean-Pierre Rampal, and he and Rampal gave the première in June 1957 at the Strasbourg Music Festival.
 It is now one of Poulenc's best known works and is a prominent feature in 20th century flute repertoire.
Achsa W. Sprague (November 17, 1827 – July 6, 1862) was one of the best-known Spiritualists during the 1850s in the United States.
 Primarily a medium and trance lecturer, she also wrote articles and poetry for Spiritualist publications such as the "Banner of Light", the "Green Mountain Sibyl", and the "People's World".

Question: What was  Achsa W. Sprague best known for?
Answer: Spiritualism