|Fair Rosamund's Well today.|
The Rosamund of the name is Rosamund Clifford, who would have been unknown to history but for an event that pushed her into prominence. Daughter of Walter Clifford, she was born sometime before 1150. Her father's position in government was sufficient that the king had reason to call on him. Sometime in 1163 (according to best guesses), Henry II did just that, stopping at Clifford Castle on the River Wye on his way to deal with a Welsh problem. That is likely where and when he first met Rosamund...
...and when they fell in love.
Henry was married—Eleanor of Aquitaine had divorced the king of France in 1152 and married Henry in 1154—but kings never let marriage stop them. There is much gossip and legend surrounding "Fair Rosamund," but there are a few things we can say for certain. One is that she was a very patient lover: given Henry's campaigns in England and on the continent, between 1163 and her death in 1176, they would not have been able to be in each other's presence for more than 2-3 years total. Stories that she traveled with him can not be substantiated by contemporary evidence.
The likelihood that she bore children for Henry is slim. Later suggestions that his son Geoffrey was hers make no sense, given that she would have had to been pregnant with Geoffrey while she was a baby.*
It is very likely that Henry kept her in Woodstock, which at the time was essentially a hunting lodge about 10 miles north of Oxford. The legend that he built a maze around it to keep her safe is untrue. It is possible, I suppose, that she really did bathe at Rosamund's Well. Blenheim Palace is just west of Woodstock, built on the grounds that once were part of the Woodstock lodge and the enclosed deer park.
She went to live in seclusion among the nuns at a monastery in Godstow in 1176, once her status as the king's mistress became known. She died shortly thereafter, and the king contributed to a family-built tomb for her at Godstow. In 1191, the bishop of Lincoln found that her tomb, situated in the choir of the church, had become a popular site for locals to leave flowers. Shocked at the veneration given to a mistress, he had her tomb moved outside the monastery. Like so many other sites, it was destroyed by another Henry known for mistresses: Henry VIII's Dissolution of the Monasteries.
*The illegitimacy of Geoffrey is not an invention; Eleanor was not his mother. The chronicler Walter Map (1140 - c.1209) claims Geoffrey's mother was someone named Ykenai.