Walking to the Trout from Port Meadow, we came across the remains of Godstow Abbey, founded in the 12th century. Not much remains aside from the chapel and the outer walls. The funny thing is that I had just been at the Ashmolean looking at some tiles - they caught my attention because they had a deer and bird pattern that my father had copied out of a book and put on my door when I was little. It stayed on my door for at least ten years. Anyway, it turns out those tiles were from Godstow Abbey.
You can read a very good overview of the history of the site here. It turns out that the Abbey was originally built on an island formed by the Thames. After the dissolution of the monasteries it became a private residence, and then a stone quarry for local residents and a pen for their cattle. While it was still an abbey, Godstow served as the home and final resting place of Henry II's mistress Rosamund Clifford.
Right now it is a very beautiful, desolate place. It seems that someone has been living in the chapel recently, judging by the debris in it.