Queensway Tunnel.

This morning we were fortunate enough to go inside one of the ventilation shafts of the Mersey tunnel and see the enormous fans that force fresh air into the system.
We then descended to the bottom half of the tunnel below the road, which was originally designed to house a separate tramway between Liverpool and Birkenhead.
Witnessing the sheer scale of the engineering exercise was a rare treat and quite breathtaking.