Warden Grotto is around 700m long and takes the Warmden Brook under South East Accrington before it joins with Woodnook Water.
We dropped in at the upstream end equipped with rope for the first waterfall. It was nicely bolted so just clipped in and went down, trying not to breach at the bottom.
After some nice stonework, things got interesting when the streambed reverted to a more natural form resulting in a series of cascades.
The culvert shrinks down slightly and emerges in a small green corridor surrounded by car parks. A short walk later and the brook enters another culvert, Superlative Nomenclature.