When I last went, the only 'recent' addition was a bricked up wall - but we're talking possibly of about 100 years ago. We took a brick out and looked through and it was filled with rubble in a slope. It would indicate steps of some sort leading down but this appeared to be in the direction of Renshaw street rather than directly towards the River. Though it may have adjoined a set of tunnels at another point in which access to the River could have been gained.