The entrance on the south bank opens immediately onto the bridge, through it you can see a short section of path before it curves away to the east. A line of torches leads up a short incline opposite before exiting to the cave beyond. The deep blue water rushing beneath the bridge breaks & for a moment a dolphin laughs up at you & is gone.
Someone has compensated for the lack of any official sign by scrawling the name of the River Alph on the wall.