This is a site I went to with rather low expectations, but which turned out to be very interesting - and the fact that I visited on a gloriously warm and sunny September day certainly helped. The huge ruins of Fountains Abbey (not all ruins, many elements are still standing) are really amazing, and give you a great picture of monastic life in the Middle Ages. You can walk among them for hours, and the abbey is probably one of the best monastic/religious sites I have seen so far. Once you have satisified your curiosity with the ruins, a pleasant walk takes you through the Studley Royal Water Garden, which was created around the ruins in the 18th century. I always wondered about the odd combination of a 12th-century monastery with a formal Baroque garden, but they fit together well and form a coherent whole. All in all, I had a great day there - just one advice if you plan to arrive by public transport: there are only a handful of buses every day (line 139 from Ripon), and only on 3 days a week, so careful planning is necessary. I went on a Saturday (taking a train from Leeds to Harrogate and continuing by bus to Ripon) and it worked out fine.