There have been a couple of reminders of this in the last few weeks. The springs which are pouring down the hillsides because of the recent heavy rain can be seen to disappear suddenly underground when they reach the lower farmland.
And secondly, yesterday we buried in the churchyard one of of those who forty years ago discovered (in modern times anyway) the entrance to the Otter Hole cave system while out 'fishing' for salmon on the River Wye with a friend. The caves should probably be far better known beyond the ranks of the caving fraternity - they are amongst the most naturally 'decorated' in Britain and for that reason, too, access is limited - but they are only accessible through a sump at low tide. [A link, including a video here]
Tradition has it that our patron saint, the Celtic hermit St Arvan, living on the borderlands in uncertain times, spent his days fishing here on the Wye.
Did he ever notice the hidden entrance to the caves, I wonder?