The old train line to mid-Wales ran up through the valley: a victim of the Beeching cuts I believe. Now where the train track was is a paved path for walkers and cyclists. But the woods are full of indicators of the valley's history. From the remains of arsenic works to the quarry, from the bell pits to the brick works, the signs are still there if you look for them.
And that's when I had my great idea.
'Let's have an adventure, George!'
'Must we?' (George prefers the familiar.)
'Yes, come on, it will be fun. We'll try and follow the river down to where we normally join it.'
Which is what we did - and when the path ran out we went river-trekking. Until we reached this.
At this point I said, 'What would Indiana Jones say now?'
'Go for it!'
(George isn't convinced.)
Then at this point, about a sixth of the way into the tunnel, as I tripped over yet another branch and slid on a slippery rock while cold water dripped down the back of my neck, I said, 'That's the last time I listen to Indy.'
I could have persevered but what if I'd fallen? I didn't have a phone so I could have just lain there and died. And George would have sat with my body slowly starving to death himself. (Yes, I can see that happening too.)
To be honest my real fear was that I'd stumble across a body. Yes, I know it's not likely but it wasn't worth taking the risk of needing lifelong therapy and never being able to venture into a tunnel again. So we turned back.
And got home in one piece.