There’s a tarmac path that runs behind the town of Kidsgrove. Cyclists use it a lot, as it’s part of the ‘Sustrans’ national cycle network.
It’s actually what’s left of a section of the now dismantled ‘Kidsgrove Loop’ railway line.
Once one realises that, then the purpose of the niches in the side of the embankment wall becomes obvious. Railway workers would scurry into them to get out of the way of any approaching train.
The same concept is applied even in today’s road tunnels. Nothing changes!