According to Coxe, you can find St Helen's Well at Thorp Arch, and people would leave tattered cloth on a nearby tree as an offering.
However, according to the website megalithix.wordpress.com, "The well is all dried up today, but its remains are about 200 yards north of the river Wharfe".
The place is said to have been a respected holy site that was venerated long before the Romans arrived. Is also said to be haunted by “padfoots and barguests and ‘that grim foul beast with clanking chain’ which on dark nights kept its vigil”. For an excellent piece on this Well, we recommend you navigate to the link below at Megalithic.
Co-ordinates:
53°54'27.3"N 1°18'52.1"W (approx)
For further information, please read Haunted Britain by Antony D. Hippisley Coxe.