Arthur Rackham, How at the Castle of Corbin a Maiden Bare in the Sangreal and Foretold the Achievements of Galahad, from The Romance of King Arthur and His Knights of the Round Table, by Alfred W Pollard, 1917. 
Source: Wikipedia.

This is a color photo.

At the center of the painting a woman in a long, loose, flowing white gown faces left, looking down at the sangreal, the holy grail, which she holds with both hands in front of her.  The grail gives off a golden light which surrounds the woman and the grail.  The woman also appears to be standing barefoot on flames.

The grail is a large, ornate goblet.  It has a pedestal bottom extending up to a large bowl with a lid that is conical, ending in a point.

The floor of the room is square tiles.  The wall behind the woman is panelled with windows at the top, the windows covered by diamond grilling.