One of my favourite things to do in London was to follow
#HiddenRivers like the Fleet, the Hackney Brook, and the Moselle. When we moved to Bangor, the guy we bought our house from told us about the river Adda, which flows underground through the middle of the town. I've walked almost all of it, I think, and there aren't many spots where you can see or hear it. Today I noticed this waterfall on Caernarfon Road that must flow into it.