Oh my goodness what an experience! The tunnel’s 5km long and the walled channel, just 8m wide, that leads into and out of it is a further 5km so a restricted passage of 10km. There’s a speed limit too of 2knots so all very organised until 2km into the tunnel ..... all the lights went out!! We had torches but without the mast we didn’t have a deck light so it was a tad tricky to negotiate our way down. Suffice to say we were very glad when ‘there was light at the end of the tunnel’!