I think people have an incorrect and false expectation that when Christianity first came to England and other northern European lands, that the people immediately eschewed, abandoned all their previous belief systems and customs. Think about how hard this would have been for people to suddenly abandon all their prior beliefs and customs in the blink of an eye.
As I understand, during the late Saxon period in England, many early Christian burials incorporated both Christian and Pegan rituals and practices – they may have not been so sure which one to follow and so and were hedging the bets by incorporating both just in case.
The Green Man
https://www.youtube.com/watch?v=yQHl2mzF1Do
Many originally pagan customs were not eliminated but incorporated into Christian traditions. Christmas trees and greens, yule logs, Easter eggs, and so on.
And don’t even get me started on some of the Norwegian Christmas traditions I grew up with, many of which while today “Christian” have some roots in ancient pagan Norse mythology.
In one of the Time Team episodes, an ancient burial was found to contain pagan inscriptions to a previously unheard-of, apparently Romano-Britain hybrid local deity, on the inside of the box, where it didn't show to those giving the deceased the Christian burial.
Pilgrimages were probably mostly or entirely pagan in origin, particularly any that have anything to do with a natural spring or well. The innocuous but odd practice of throwing pennies into fountains is very ancient.